JEE Chemistry S Block Elements MCQs Set 04

Chemistry Objective Questions and Answers: S Block Elements

Access targeted multiple-choice questions for S Block Elements designed to align with the latest JEE academic syllabus for JEE Chemistry. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

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Multiple Choice Questions

Question 1: Which of the following is paramagnetic?
(a) K2O
(b) K2O2
(c) KO2
(d) Na2O
Show Answer & Explanation

Answer: (c) KO2

Explanation:
1. KO2 contains O2-, which has one unpaired electron
2. The others have no unpaired electrons

Teacher's Note:
1. Superoxides are paramagnetic and coloured.

Question 2: A compound that releases ammonia on hydrolysis is:
(a) Li3N
(b) LiNO3
(c) NaNO3
(d) none of these
Show Answer & Explanation

Answer: (a) Li3N

Explanation:
1. Li3N + 3H2O gives 3LiOH + NH3

Teacher's Note:
1. Nitrides give ammonia with water.

Question 3: The metal ion which does not give any flame colouration is:
(a) Li+
(b) Be2+
(c) Na+
(d) K+
Show Answer & Explanation

Answer: (b) Be2+

Explanation:
1. Be2+ has a very high excitation energy
2. So it gives no colour

Teacher's Note:
1. Be and Mg do not impart colour.

Question 4: Which of the following exists as a hydrated salt?
(a) NaCl
(b) LiCl
(c) RbCl
(d) KCl
Show Answer & Explanation

Answer: (b) LiCl

Explanation:
1. Li+ is highly hydrated
2. LiCl crystallises as LiCl.2H2O

Teacher's Note:
1. Other alkali chlorides are anhydrous.

Question 5: The strong reductant in IIA and IA group is:
(a) Ba, Li
(b) Li, Be
(c) Cs, Ba
(d) Ba, Cs
Show Answer & Explanation

Answer: (a) Ba, Li

Explanation:
1. Ba is the strongest reductant in group 2
2. Li has the most negative reduction potential in group 1

Teacher's Note:
1. Hydration energy makes Li the strongest in water.

Question 6: Which statement is true for a solution when Ba is dissolved in ammonia?
(a) the solution becomes blue
(b) the solution becomes a good conductor
(c) the solution remains colourless
(d) both (a) and (b) are correct
Show Answer & Explanation

Answer: (d) both (a) and (b) are correct

Explanation:
1. Alkaline earth metals dissolve in liquid NH3 giving blue solutions
2. The ammoniated electrons and ions make it conducting

Teacher's Note:
1. Solvated electrons cause the blue colour.

Question 7: In K, Rb and Cs, the decreasing order of reducing power in the gaseous state is:
(a) K > Cs > Rb
(b) Cs > Rb > K
(c) K < Cs < Rb
(d) Rb > Cs > K
Show Answer & Explanation

Answer: (b) Cs > Rb > K

Explanation:
1. Ionisation energy decreases from K to Cs
2. So reducing power in gaseous state is Cs > Rb > K

Teacher's Note:
1. Gaseous state follows ionisation energy.

Question 8: The correct order of density of the elements Be, Mg, Ca, Sr is:
(a) Be > Mg > Ca > Sr
(b) Ca > Mg > Be > Sr
(c) Ca < Mg < Be < Sr
(d) Mg < Ca < Sr < Be
Show Answer & Explanation

Answer: (c) Ca < Mg < Be < Sr

Explanation:
1. Densities: Ca 1.55, Mg 1.74, Be 1.85, Sr 2.6 g/cm3

Teacher's Note:
1. Density does not vary regularly.

Question 9: Identify the correct statement for elemental sodium:
(a) it is a strong oxidising agent
(b) it can be extracted by electrolysis of aqueous solution
(c) its density is lower than K
(d) it is easily oxidised
Show Answer & Explanation

Answer: (d) it is easily oxidised

Explanation:
1. Na is a strong reducing agent, so it is easily oxidised
2. It is obtained from molten NaCl, and its density is higher than K

Teacher's Note:
1. Alkali metals are reducing agents.

Question 10: On addition of a metal, the colour of liquid NH3 solution changes to bronze. The reason is:
(a) ammoniated electrons
(b) metal amide formation
(c) liberation of NH3 gas
(d) cluster formation of metal ions
Show Answer & Explanation

Answer: (d) cluster formation of metal ions

Explanation:
1. Concentrated solutions form metal ion clusters
2. The solution is bronze and diamagnetic

Teacher's Note:
1. Dilute solutions are blue.

Question 11: On allowing an ammonia solution of s-block metals to stand for a long time, the blue colour fades. The reason is:
(a) formation of NH3 gas
(b) formation of metal amide
(c) cluster formation of metal ions
(d) formation of metal nitrate
Show Answer & Explanation

Answer: (b) formation of metal amide

Explanation:
1. M + NH3 slowly gives MNH2 + H2
2. The amide formation removes the solvated electrons

Teacher's Note:
1. The reaction is slow without a catalyst.

Question 12: Which s-block element reacts with NaOH to give a water soluble complex?
(a) Al
(b) Ca
(c) Be
(d) Li
Show Answer & Explanation

Answer: (c) Be

Explanation:
1. Be + 2NaOH + 2H2O gives Na2[Be(OH)4] + H2
2. Be is amphoteric

Teacher's Note:
1. Al is not an s-block element.

Question 13: Which has the least melting point?
(a) Ba
(b) Ca
(c) Mg
(d) Be
Show Answer & Explanation

Answer: (c) Mg

Explanation:
1. Melting points (K): Be 1560, Ca 1115, Ba 1000, Mg 923
2. Mg is the lowest

Teacher's Note:
1. Group 2 melting points are irregular.

Question 14: When Na and Li are placed in dry air, we get:
(a) NaOH, Na2O, Li2O
(b) Na2CO3, Na2O2, Li2O
(c) Na2O, Li3N, NH3
(d) Na2O, Li2O, Li3N
Show Answer & Explanation

Answer: (d) Na2O, Li2O, Li3N

Explanation:
1. Na gives mainly Na2O (and Na2O2), Li gives Li2O and also Li3N with the nitrogen of air

Teacher's Note:
1. Dry air has no CO2 or moisture in effect.

Question 15: Which of the following oxides contains the O2 2- (peroxide) anion?
(a) Na2O
(b) BaO2
(c) RbO2
(d) KO2
Show Answer & Explanation

Answer: (b) BaO2

Explanation:
1. BaO2 contains the peroxide ion
2. RbO2 and KO2 are superoxides

Teacher's Note:
1. Peroxide ion is O2 2-.

Question 16: Which of the following properties of IA group metals increases as the atomic number rises? (a) metallic character (b) ionic radius (c) melting point (d) density (e) ionisation potential
(a) a, b, c
(b) a, b, d
(c) c, d, e
(d) all
Show Answer & Explanation

Answer: (b) a, b, d

Explanation:
1. Metallic character, ionic radius and density generally increase down the group
2. Melting point and ionisation energy decrease

Teacher's Note:
1. Check each property separately.

Question 17: Which of the following s-block metals do not impart any colour to the flame?
(a) Li, Be
(b) Cs, Fr
(c) Be, Mg
(d) Ba, Ra
Show Answer & Explanation

Answer: (c) Be, Mg

Explanation:
1. Be and Mg have very high excitation energies
2. So they give no flame colour

Teacher's Note:
1. Others give characteristic colours.

Question 18: Which cannot be used to generate H2?
(a) Al + NaOH
(b) Zn + NaOH
(c) Mg + NaOH
(d) LiH + H2O
Show Answer & Explanation

Answer: (c) Mg + NaOH

Explanation:
1. Mg is not amphoteric and does not react with NaOH
2. The others produce H2

Teacher's Note:
1. Zn and Al are amphoteric.

Question 19: Only those s-block elements can produce superoxides which have:
(a) high ionisation energy
(b) high electronegativity
(c) high charge density
(d) low ionisation potential
Show Answer & Explanation

Answer: (d) low ionisation potential

Explanation:
1. Large, low-ionisation cations (K, Rb, Cs) stabilise the large O2-
2. So they form superoxides

Teacher's Note:
1. Large cations stabilise large anions.

Question 20: Which does not exist in solid state?
(a) LiHCO3
(b) CaCO3
(c) NaHCO3
(d) Na2CO3
Show Answer & Explanation

Answer: (a) LiHCO3

Explanation:
1. LiHCO3 exists only in solution
2. Bicarbonates of the others are stable solids

Teacher's Note:
1. Li shows anomalous behaviour.

Question 21: When alkali metals dissolve in liquid NH3, which of the following observations is not true?
(a) it becomes paramagnetic
(b) the solution turns blue due to solvated electrons
(c) it becomes diamagnetic
(d) the solution becomes conducting
Show Answer & Explanation

Answer: (c) it becomes diamagnetic

Explanation:
1. Dilute solutions are paramagnetic because of free solvated electrons
2. So 'it becomes diamagnetic' is not true

Teacher's Note:
1. Concentrated solutions may be diamagnetic, but it is not a general statement.

Question 22: Alkali metals give colour in a Bunsen flame due to:
(a) low electronegativity
(b) one electron in the outermost orbit
(c) smaller atomic radii
(d) low ionisation energy
Show Answer & Explanation

Answer: (d) low ionisation energy

Explanation:
1. Low ionisation energy lets the outer electron be excited by the flame
2. The emission appears as colour

Teacher's Note:
1. Excitation needs little energy.

Question 23: Which of the following ions forms a hydroxide that is highly soluble in water?
(a) K+
(b) Zn2+
(c) Ni2+
(d) Al3+
Show Answer & Explanation

Answer: (a) K+

Explanation:
1. KOH is a strong base and highly soluble
2. Others are sparingly soluble or amphoteric

Teacher's Note:
1. Alkali metal hydroxides dissolve freely.

Question 24: Slaked lime is made by adding water to:
(a) quick lime
(b) nitrolim
(c) limestone
(d) plaster of Paris
Show Answer & Explanation

Answer: (a) quick lime

Explanation:
1. CaO + H2O gives Ca(OH)2

Teacher's Note:
1. The process is exothermic.

Question 25: Plaster of Paris is hardened by:
(a) liberating CO2
(b) giving out water
(c) combining with water
(d) changing into CaCO3
Show Answer & Explanation

Answer: (c) combining with water

Explanation:
1. CaSO4.1/2H2O + 3/2 H2O gives CaSO4.2H2O (gypsum), which sets hard

Teacher's Note:
1. Setting is hydration.

Question 26: Which of the following alkali metal carbonates is the least stable and decomposes readily?
(a) Li2CO3
(b) Na2CO3
(c) K2CO3
(d) Cs2CO3
Show Answer & Explanation

Answer: (a) Li2CO3

Explanation:
1. Li+ is small and polarises CO3 2- strongly
2. Li2CO3 decomposes to Li2O and CO2

Teacher's Note:
1. Stability rises down the group.

Question 27: In the reaction M + O2 gives MO2 (superoxide), the metal is:
(a) Li
(b) Na
(c) K
(d) Ba
Show Answer & Explanation

Answer: (c) K

Explanation:
1. K, Rb and Cs form superoxides
2. Li gives oxide, Na gives peroxide

Teacher's Note:
1. Large cations stabilise the superoxide.

Question 28: Li does not resemble other alkali metals in which of the following properties?
(a) Li2CO3 decomposes into oxides while other alkali carbonates are thermally stable
(b) LiCl is predominantly covalent
(c) Li3N is stable
(d) all of these
Show Answer & Explanation

Answer: (d) all of these

Explanation:
1. All three show lithium's anomalous behaviour due to small size and high polarising power

Teacher's Note:
1. Li resembles Mg (diagonal relationship).

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