ICSE Class 10 Chemistry Board Exam Question Paper 2015 with Solutions

ICSE Board Class X Chemistry Board Exam Question Paper with Solutions

SECTION I (40 Marks)

Attempt all questions from this Section

(1) Select from the list the gas that matches the description given in each case: [5]
[ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne]
(i) This gas is used as a reducing agent in reducing copper oxide to copper.
(ii) This gas produces dense white fumes with ammonia gas.
(iii) This gas is used for welding purposes.
(iv) This gas is also a saturated hydrocarbon.
(v) This gas has a characteristic rotten egg smell.

Answer:
(i) Ammonia
(ii) Hydrogen chloride
(iii) Ethyne
(iv) Ethane
(v) Hydrogen sulphide

Teacher's Note:
a) Know the specific physical and chemical properties of common gases like ammonia and hydrogen chloride.
b) Ethane is a saturated hydrocarbon (alkane), whereas ethyne is an unsaturated hydrocarbon (alkyne) used in oxy-acetylene welding.

(2) Choose the most appropriate answer for each of the following: [1]
(i) Among the elements given below, the element with the least electro negativity is:
(A) Lithium
(B) Carbon
(C) Boron
(D) Fluorine

Answer: (A) Lithium

Lithium has the lowest electronegativity among the given elements as it is an alkali metal located on the extreme left of the Periodic Table.

Teacher's Note:
a) Electronegativity increases across a period from left to right and decreases down a group.
b) Fluorine is the most electronegative element in the entire periodic table.

(3) Identify the statement which does not describe the property of alkenes: [1]
(A) They are unsaturated hydrocarbons
(B) They decolourise bromine water
(C) They can undergo addition as well as substitution reactions
(D) They undergo combustion with oxygen forming carbon dioxide and water.

Answer: (C) They can undergo addition as well as substitution reactions

Alkenes undergo addition reactions due to the presence of a double bond, but they do not typically undergo substitution reactions (which are characteristic of alkanes).

Teacher's Note:
a) Unsaturated hydrocarbons characteristically undergo addition reactions.
b) Alkanes undergo substitution reactions, whereas alkenes and alkynes undergo addition reactions.

(4) This is not an alloy of copper: [1]
(A) Brass
(B) Bronze
(C) Solder
(D) Duralumin.

Answer: (C) Solder

Solder is an alloy of lead and tin, not copper.

Teacher's Note:
a) Brass is an alloy of copper and zinc; bronze is an alloy of copper and tin.
b) Duralumin contains aluminium, copper, magnesium, and manganese.

(5) Bonding in this molecule can be understood to involve coordinate bonding. [1]
(A) Carbon tetrachloride
(B) Hydrogen
(C) Hydrogen chloride
(D) Ammonium chloride

Answer: (D) Ammonium chloride

Ammonium chloride contains an ionic bond between ammonium and chloride ions, covalent bonds within the ammonium ion, and a coordinate (dative) bond between the nitrogen atom of ammonia and the hydrogen ion (proton).

Teacher's Note:
a) A coordinate bond is formed by a shared pair of electrons where both electrons come from the same atom.
b) The formation of the ammonium ion from ammonia and a hydrogen ion is a classic example of coordinate bonding.

(6) Which of the following would weigh the least? [1]
(A) 2 gram atoms of Nitrogen.
(B) 1mole of Silver
(C) 22.4 litres of oxygen gas at 1 atmospheric pressure and 273K
(D) 6.02×10²³ atoms of carbon.
[Atomic masses: Ag=108, N=14, O=16, C=12]

Answer: (A) 2 gram atoms of Nitrogen.

Mass of 2 gram atoms of Nitrogen = 2 × 14 g = 28 g. Mass of 1 mole of Silver = 108 g. Mass of 22.4 L of oxygen gas at S.T.P. = 32 g. Mass of 6.02 × 10²³ atoms of carbon = 12 g. Wait, 12 g is less than 28 g? Let us check properly: 6.02 × 10²³ atoms of carbon is 1 mole of carbon = 12 g. 2 gram atoms of Nitrogen is 2 moles of N atoms = 28 g. 22.4 L of O₂ gas is 1 mole of O₂ molecules = 32 g. 1 mole of Silver = 108 g. Therefore, 6.02 × 10²³ atoms of carbon weighs 12 g which is the least among all options.

Teacher's Note:
a) The official key shows (A); however, 6.02 × 10²³ atoms of carbon weighs 12 grams whereas 2 gram atoms of nitrogen weigh 28 grams. The correct answer is (D) because 12 grams is less than 28 grams, 32 grams, and 108 grams.
b) Students must carefully convert each term into mass in grams using atomic and molar masses to compare them accurately.

(7) Complete the following calculations. Show working for complete credit:
(i) Calculate the mass of Calcium that will contain the same number of atom as are present in 3.2 gm of Sulphur.
[Atomic masses: S=32, Ca=40] [2]
(ii) If 6 litres of hydrogen and 4 litres of chlorine are mixed and exploded and if water is added to the gases formed, find the volume of the residual gas. [2]
(iii) If the empirical formula of a compound is CH and it has a vapour density of 13, find the molecular formula of the compound. [1]

Answer:
(i) Moles of Sulphur = \(3.2 \div 32 = 0.1\) moles.
Number of atoms in 0.1 moles of Sulphur = \(0.1 \times N_A\).
For Calcium to have the same number of atoms, it must also be 0.1 moles.
Mass of Calcium = Moles × Atomic Mass = \(0.1 \times 40 = 4\) g.
(ii) Equation: \(H_2 + Cl_2 \rightarrow 2HCl\)
1 volume of hydrogen reacts with 1 volume of chlorine to give 2 volumes of hydrogen chloride.
4 litres of chlorine will react with 4 litres of hydrogen to give 8 litres of \(HCl\) gas.
Unreacted hydrogen remaining = \(6 - 4 = 2\) litres.
When water is added, \(HCl\) dissolves completely in water.
Therefore, the volume of the residual gas is 2 litres of hydrogen.
(iii) Molecular Mass = 2 × Vapour Density = \(2 \times 13 = 26\).
Empirical formula mass of \(CH = 12 + 1 = 13\).
\(n = \text{Molecular Mass} \div \text{Empirical Formula Mass} = 26 \div 13 = 2\).
Molecular formula = \((CH)_n = C_2H_2\).

Teacher's Note:
a) Use the mole concept to equate number of atoms or moles across different elements.
b) Remember that hydrogen chloride gas is highly soluble in water, leaving behind any unreacted excess reactant.

State one relevant observation for each of the following:
(8) When crystals of copper nitrate are heated in a test tube.[1]
(9) When the gaseous product obtained by dehydration of ethyl alcohol is passed through bromine water[1]
(10) When hydrogen sulphide gas is passed through lead acetate solution.[1]
(11) When ammonia gas is burnt in an atmosphere of excess oxygen.[1]
(12) At the Anode when aqueous copper sulphate solution is electrolyzed using copper electrodes. [1]

Answer:
(8) A reddish brown gas (nitrogen dioxide) is evolved and a black residue (copper oxide) is left behind.
(9) Reddish-brown bromine water gets decolourised (turns colourless).
(10) A black precipitate of lead sulphide is formed.
(11) Ammonia burns with a greenish-yellow flame producing nitrogen gas and water vapour.
(12) The copper anode dissolves (decreases in mass) releasing copper ions into the solution.

Teacher's Note:
a) Be precise with colour changes, such as reddish-brown gas or black precipitate.
b) In electrolysis with active copper electrodes, the anode undergoes oxidation and dissolves.

(13) Identify the acid which matches the following description (i) to (v):
(i) The acid which is used in the preparation of a non-volatile acid. [1]
(ii) The acid which produces sugar charcoal from sugar. [1]
(iii) The acid which is prepared by catalytic oxidation of ammonia. [1]
(iv) The acid on mixing with lead nitrate solution produces a white precipitate which is insoluble even on heating. [1]
(v) The acid on mixing with silver nitrate solution produces a white precipitate which is soluble in excess ammonium hydroxide. [1]

Answer:
(i) Concentrated Sulphuric acid
(ii) Concentrated Sulphuric acid
(iii) Nitric acid
(iv) Sulphuric acid
(v) Hydrochloric acid

Teacher's Note:
a) Concentrated sulphuric acid is non-volatile and is used to prepare volatile acids like HCl and \(HNO_3\).
b) Concentrated sulphuric acid is a strong dehydrating agent that chars cane sugar to carbon.

Give appropriate scientific reasons for the following statements:
(14) Zinc oxide can be reduced to zinc by using carbon monoxide, but aluminium oxide cannot be reduced by a reducing agent [1]
(15) Carbon tetrachloride does not conduct electricity. [1]
(16) During electrolysis of molten lead bromide graphite anode is preferred to other electrodes. [1]
(17) The electrical conductivity of acetic acid is less in comparison to the electrical conductivity of dilute sulphuric acid at a given concentration. [1]
(18) Electrolysis is of molten lead bromide is considered to be a redox reaction. [1]

Answer:
(14) Aluminium has a very high affinity for oxygen and lies much higher up in the reactivity series than zinc, hence its oxide cannot be reduced by common reducing agents like carbon or carbon monoxide.
(15) Carbon tetrachloride is a covalent compound and does not contain free ions to carry electric current.
(16) Graphite anode is inert and does not react with the corrosive bromine vapours liberated at the anode during electrolysis.
(17) Acetic acid is a weak electrolyte that dissociates only partially in aqueous solution, whereas sulphuric acid is a strong electrolyte that dissociates almost completely, yielding a much higher concentration of ions.
(18) During the electrolysis of molten lead bromide, lead ions undergo reduction (gain of electrons) at the cathode while bromide ions undergo oxidation (loss of electrons) at the anode, making it a redox reaction.

Teacher's Note:
a) Metals high in the reactivity series like aluminium require electrolytic reduction.
b) Redox reactions involve simultaneous oxidation and reduction half-reactions.

(19) Give balanced chemical equations for the following conversions A, B and C:
\(Fe \xrightarrow{A} FeCl_3 \xrightarrow{B} FeCO_3 \xrightarrow{C} Fe(NO_3)_2\) [1]

Answer:
A: \(2Fe + 3Cl_2 \rightarrow 2FeCl_3$
B: \(FeCl_3 + 3NaHCO_3 \rightarrow FeCO_3 + 3NaCl + H_2O + CO_2\) (or reaction with soluble carbonate/bicarbonate giving iron carbonate)
C: \(FeCO_3 + 2HNO_3 \rightarrow Fe(NO_3)_2 + H_2O + CO_2\)

Teacher's Note:
a) Ensure all chemical equations are fully balanced with correct physical states or formulae.
b) Conversion steps require choosing appropriate reagents for displacement or double decomposition reactions.

(20) Differentiate between the terms strong electrolyte and weak electrolyte. (stating any two differences) [1]

Answer:

Teacher's Note:
a) Differences should clearly cover degree of dissociation and conducting ability.
b) Examples include hydrochloric acid for strong electrolytes and acetic acid for weak electrolytes.

Answer the following questions:
(21) Explain the bonding in methane molecule using electron dot structure. [2]
(22) The metal of Group 2 from top to bottom are Be, Mg, Ca, Sr, and Ba.
(1) Which one of these elements will form ions most readily and why?
(2) State the common feature in the electronic configuration of all these elements. [3]

Answer:
(21) In a methane molecule (\(CH_4\)), the carbon atom shares its four valence electrons with four hydrogen atoms. Carbon completes its octet and each hydrogen completes its duplet by mutual sharing of electrons, forming four single covalent bonds.
(22) (1) Barium (Ba) will form ions most readily because atomic size increases down the group, nuclear pull decreases, and the valence electrons are easily lost.
(2) All these elements have 2 valence electrons in their outermost shell.

Teacher's Note:
a) Electron dot structures should clearly show shared pairs of electrons between atoms.
b) Down a group, metallic character and ease of losing electrons increase due to increasing atomic radius.

SECTION II (40 Marks)

Attempt any four questions from this Section

(23) Arrange the following as per the instructions given in the brackets:
(i) Cs, Na, Li, K, Rb (increasing order of metallic character).
(ii) Mg, Cl, Na, S, Si (decreasing order of atomic size).
(iii) Na, K, Cl, S, Si (increasing order ionization energy)
(iv) Cl, F, Br, I (increasing order of electron affinity) [4]

Answer:
(i) Li < Na < K < Rb < Cs
(ii) Na > Mg > Si > S > Cl
(iii) K < Na < Si < S < Cl
(iv) I < Br < F < Cl

Teacher's Note:
a) Metallic character increases down a group and decreases across a period from left to right.
b) Chlorine has an exceptionally higher electron affinity than fluorine due to small size electron-electron repulsion in fluorine.

(24) Choose the most appropriate answer from the following list of oxides which fit the description. Each answer may be used only once:
[SO₂, SiO₂, Al₂O₃, MgO, CO, Na₂O]
(i) A basic oxide.
(ii) An oxide which dissolves in water forming an acid.
(iii) An amphoteric oxide.
(iv) A covalent oxide of a metalloid. [4]

Answer:
(i) \(Na_2O$
(ii) \(SO_2$
(iii) \(Al_2O_3$
(iv) \(SiO_2$

Teacher's Note:
a) Metallic oxides are generally basic, while non-metallic oxides are acidic.
b) Amphoteric oxides react with both acids and alkalis to form salt and water.

(25) Element X is a metal with a valency 2, Y is a non-metal with a valency 3.
(i) Write an equation to show how Y forms an ion.
(ii) If Y is a diatomic gas, write an equation for the direct combination of X and Y to form a compound. [2]

Answer:
(i) \(Y + 3e^- \rightarrow Y^{3-}$
(ii) \(3X + 2Y_2 \rightarrow X_3Y_2$

Teacher's Note:
a) Non-metals gain electrons to form negatively charged anions.
b) Cross-valency method gives the formula of the compound as \(X_3Y_2\).

(26) Give balanced chemical equations for the following conversions:
(i) Ethanoic acid to ethyl ethanoate.
(ii) Calcium carbide to ethyne.
(iii) Sodium ethanoate to methane. [3]

Answer:
(i) \(CH_3COOH + C_2H_5OH \xrightarrow{conc. H_2SO_4} CH_3COOC_2H_5 + H_2O$
(ii) \(CaC_2 + 2H_2O \rightarrow Ca(OH)_2 + C_2H_2$
(iii) \(CH_3COONa + NaOH \xrightarrow{CaO, \Delta} Na_2CO_3 + CH_4\)

Teacher's Note:
a) Esterification takes place in the presence of concentrated sulphuric acid as a dehydrating catalyst.
b) Decarboxylation of sodium ethanoate with sodalime produces methane gas.

(27) Using their structural formulae identify the functional group by circling them:
(i) Dimethyl ether.
(ii) Propanone.
(c) Name the following:
(i) Process by which ethane is obtained from ethene.
(ii) A hydrocarbon which contributes towards the greenhouse effect.
(iii) Distinctive reaction that takes place when ethanol is treated with acetic acid.
(iv) The property of element by virtue of which atoms of the element can link to each other in the form of a long chain or ring structure.
(v) Reaction when an alkyl halide is treated with alcoholic potassium hydroxide. [5]

Answer:
(i) Ether functional group (\(-O-\))
(ii) Ketone functional group (\(-CO-\))
(c)
(i) Catalytic hydrogenation
(ii) Methane
(iii) Esterification
(iv) Catenation
(v) Dehydrohalogenation (Elimination reaction)

Teacher's Note:
a) Functional groups determine the characteristic chemical properties of organic compounds.
b) Catenation is the unique ability of carbon atoms to form long chains and rings.

(28) Identify the anion present in each of the following compounds:
(i) A salt M on treatment with concentrated sulphuric acid produces a gas which fumes in moist air and gives dense fumes with ammonia.
(ii) A salt D on treatment with dilute sulphuric acid produces a gas which turns lime water milky but has no effect on acidified potassium dichromate solution.
(iii) When barium chloride solution is added to salt solution E a white precipitate insoluble in dilute hydrochloric acid is obtained. [3]

Answer:
(i) Chloride ion (\(Cl^-\))
(ii) Carbonate ion (\(CO_3^{2-}\))
(iii) Sulphate ion (\(SO_4^{2-}\))

Teacher's Note:
a) Chloride salts react with concentrated sulphuric acid to give hydrogen chloride gas which gives dense white fumes with ammonia.
b) Carbonates react with dilute acids to release carbon dioxide gas which turns lime water milky.

(29) The following table shows the test a student performed on four different aqueous solutions which are X, Y, Z and W. Based on the observations provided, identify them

(c) Give balanced chemical equations for each of the following:
(i) Lab preparation of ammonia using an ammonium salt
(ii) Reaction of ammonia with excess chlorine.
(iii) Reaction of ammonia with sulphuric acid. [3]

Answer:
(i) Zinc salt / Zinc ions (\(Zn^{2+}\))
(ii) Copper salt / Copper ions (\(Cu^{2+}\))
(iii) Calcium salt / Calcium ions (\(Ca^{2+}\))
(iv) Ammonium salt / Ammonium ion (\(NH_4^+\))
(c)
(i) \(2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3$
(ii) \(8NH_3 + 3Cl_2 \rightarrow N_2 + 6NH_4Cl$
(iii) \(2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4\)

Teacher's Note:
a) Analytical chemistry tables are based on characteristic precipitate colours and solubilities in excess reagents.
b) Ammonia reacts with excess chlorine to form nitrogen gas and hydrogen chloride which forms ammonium chloride fumes.

(30) Consider the following reaction and based on the reaction answer the questions that follow:
\((NH_4)_2Cr_2O_7 \rightarrow N_2(g) + 4H_2O(g) + Cr_2O_3$
Calculate:
(i) the quantity in moles of \((NH_4)_2Cr_2O_7\) if 63gm of \((NH_4)_2Cr_2O_7\) is heated. [1]
(ii) the quantity in moles of nitrogen formed. [1]
(iii) the volume in litres or dm³ of \(N_2\) evolved at S.T.P. [1]
(iv) the mass in grams of \(Cr_2O_3\) formed at the same time. [2]
(Atomic masses: H=1, Cr= 52, N=14, O=16]

Answer:
Molar mass of \((NH_4)_2Cr_2O_7 = (2 \times 18) + (2 \times 52) + (7 \times 16) = 36 + 104 + 112 = 252\) g/mol.
(i) Moles of \((NH_4)_2Cr_2O_7 = 63 \div 252 = 0.25\) moles.
(ii) From the balanced equation, 1 mole of \((NH_4)_2Cr_2O_7\) gives 1 mole of \(N_2\).
Moles of \(N_2\) formed = 0.25 moles.
(iii) Volume of \(N_2\) at S.T.P. = \(0.25 \times 22.4 = 5.6\) litres.
(iv) Molar mass of \(Cr_2O_3 = (2 \times 52) + (3 \times 16) = 104 + 48 = 152\) g/mol.
Mass of \(Cr_2O_3\) formed = \(0.25 \times 152 = 38\) grams.

Teacher's Note:
a) Always calculate the molar mass of the given reactant accurately before finding moles.
b) Use stoichiometric coefficients from the balanced equation to relate moles of reactants and products.

(31) For each of the substance listed below, describe the role played in the extraction of aluminium.
(1) Cryolite
(2) Sodium hydroxide
(3) Graphite [3]
(ii) Explain why:
(1) In the electrolysis of alumina using the Hall Heroult's Process the electrolyte is covered with powdered coke.
(2) Iron sheets are coated with zinc during galvanization. [2]

Answer:
(i)
(1) Cryolite acts as a solvent for fused alumina, lowers its fusion point, and increases electrical conductivity.
(2) Sodium hydroxide is used in Baeyer's process to leach alumina from bauxite ore, dissolving it as sodium meta-aluminate while impurities remain insoluble.
(3) Graphite acts as the anode in the electrolytic cell, which gets oxidized to carbon dioxide gas during the process.
(ii)
(1) Powdered coke is spread over the electrolyte to prevent heat loss by radiation and to prevent the burning (oxidation) of the carbon anodes by air.
(2) Zinc is more reactive than iron; it forms a protective oxide layer and acts as a sacrificial anode, preventing the underlying iron from rusting.

Teacher's Note:
a) Metallurgy of aluminium involves concentration, Hall-Heroult electrolytic reduction, and purification.
b) Galvanization protects iron by sacrificial protection since zinc corrodes in preference to iron.

(32)
(i) Give balanced chemical equations for the action of sulphuric acid on each of the following:
(1) Potassium hydrogen carbonate.
(2) Sulphur.
(ii) In the contact process for the manufacture of sulphuric acid give the equations for the conversion of sulphur trioxide to sulphuric acid. [2]

Answer:
(i)
(1) \(KHCO_3 + H_2SO_4 \rightarrow KHSO_4 + H_2O + CO_2$
(2) \(S + 2H_2SO_4 (conc.) \rightarrow 3SO_2 + 2H_2O$
(ii)
\(SO_3 + H_2SO_4 \rightarrow H_2S_2O_7\) (Oleum)
\(H_2S_2O_7 + H_2O \rightarrow 2H_2SO_4\)

Teacher's Note:
a) Concentrated sulphuric acid acts as an oxidizing agent when reacted with non-metals like sulphur.
b) In the contact process, sulphur trioxide is dissolved directly in concentrated sulphuric acid to form oleum rather than water to avoid forming dense acid mist.

(33) Copy and complete the following table:

(ii) Write the equation taking place at the anode. [1]

Answer:
(i)
Anode: Impure copper
Electrolyte: Acidified copper sulphate solution
(ii) \(Cu - 2e^- \rightarrow Cu^{2+}\)

Teacher's Note:
a) In electrorefining of copper, the impure copper strip is made the anode and pure copper strip is the cathode.
b) Copper atoms lose electrons at the anode to enter the solution as copper ions.

(34) Explain the following:
(i) Dilute nitric acid is generally considered a typical acid but not so in its reaction with metals.
(ii) Concentrated nitric acid appears yellow when it is left standing in a glass bottle.
(iii) An all glass apparatus is used in the laboratory preparation of nitric acid. [3]

Answer:
(i) Dilute nitric acid is a strong oxidizing agent, and when it reacts with metals, it typically releases hydrogen and then oxidizes it to water, thus generally producing nitrogen oxides instead of hydrogen gas.
(ii) Concentrated nitric acid undergoes thermal decomposition in sunlight to form dissolved nitrogen dioxide gas, which imparts a yellowish-brown colour to the acid.
(iii) An all-glass apparatus is used because nitric acid vapours are highly corrosive and attack cork or rubber stoppers.

Teacher's Note:
a) Nitric acid is a powerful oxidizing agent due to the ease with which it releases nascent oxygen.
b) Glass is resistant to the corrosive action of nitric acid vapours.

(35) The following questions are pertaining to the laboratory preparation of hydrogen chloride gas:
(i) Write the equation for its preparation mentioning the condition required. [1]
(ii) Name the drying agent used and justify your choice. [2]
(iii) State a safety precaution you would take during the preparation of hydrochloric acid. [1]

Answer:
(i) \(NaCl + H_2SO_4 \xrightarrow{\lt 200^{\circ}C} NaHSO_4 + HCl\)
(ii) Concentrated sulphuric acid is used as a drying agent because it is a strong dehydrating agent and does not react chemically with hydrogen chloride gas.
(iii) The temperature should be maintained below 200 degrees Celsius to avoid damaging the glass apparatus and forming hard crusts of sodium sulphate.

Teacher's Note:
a) Temperature control below 200°C is crucial in the laboratory preparation of HCl.
b) Calcium oxide or phosphorus pentoxide cannot be used as drying agents because they react chemically with hydrogen chloride.

(36) An element L consists of molecules.
(i) What type of bonding is present in the particles that make up L?
(ii) When L is heated with iron metal, it forms a compound FeL. What chemical term would you use to describe the change undergone by L? [2]

Answer:
(i) Covalent bonding
(ii) Oxidation (or combination)

Teacher's Note:
a) Non-metallic elements forming discrete molecules contain covalent bonds.
b) Reaction of a metal with a non-metal resulting in the addition of the non-metal is an oxidation process.

(37) From the list of the following salts choose the salt that most appropriately fits the description given in the following:
[AgCl, \(MgCl_2\), \(NaHSO_4\), \(PbCO_3\), \(ZnCO_3\), \(KNO_3\), \(Ca(NO_3)_2\)]
(i) A deliquescent salt.
(ii) An insoluble chloride.
(iii) On heating, this salt gives a yellow residue when hot and white when cold.
(iv) On heating this salt, a brown coloured gas is evolved. [4]

Answer:
(i) \(MgCl_2$
(ii) \(AgCl$
(iii) \(ZnCO_3$
(iv) \(Ca(NO_3)_2\)

Teacher's Note:
a) Deliquescent salts absorb moisture from the atmosphere and dissolve in it.
b) Zinc oxide is yellow when hot and white when cold, which is observed upon heating zinc carbonate.