CBSE Class 10 Chemistry Metals and Non-metals MCQs Set 38

Answer: (a) calcium

Explanation:
1. A compound with a high melting point and solubility in water is ionic.
2. Calcium forms CaO, an ionic oxide with a high melting point that reacts with water to give Ca(OH)₂ which dissolves slightly.
3. CO₂ and SiO₂ are covalent, and iron oxides are insoluble.

Teacher's Note:
1. Ionic compounds have high melting points because of strong electrostatic forces.
2. Metals of group 2 form ionic oxides.

Answer: (b) a covalent chloride

Explanation:
1. Non-metals do not lose electrons easily, so they share electrons with chlorine.
2. The chloride formed is covalent (for example CCl₄, PCl₃).

Teacher's Note:
1. Metals form ionic chlorides such as NaCl.
2. Covalent chlorides are volatile and non-conducting.

Answer: (a) froth floatation

Explanation:
1. Sulphide ores are concentrated by froth floatation, where the ore particles stick to the froth made with pine oil and the gangue sinks.
2. Roasting converts the ore into oxide, which is a later step.

Teacher's Note:
1. Sulphide ores are wetted by oil, gangue is wetted by water.
2. Pine oil is the froth stabiliser.

Answer: (a) gold

Explanation:
1. Gold is very unreactive and does not combine with oxygen or sulphur, so it occurs native.
2. Sodium is very reactive; silver and copper occur both free and combined.

Teacher's Note:
1. Platinum is another metal found in the free state.
2. Reactive metals are found as compounds.

Answer: (a) zero

Explanation:
1. The 'lead' of a pencil is graphite mixed with clay and contains no lead.
2. So the percentage of lead is zero.

Teacher's Note:
1. The name is historical.
2. Graphite is a form of carbon.

Answer: (c) both an oxidising agent and a dehydrating agent

Explanation:
1. It removes water from sugar and from many compounds, so it is a dehydrating agent.
2. It also oxidises copper, carbon and sulphur on heating, so it is an oxidising agent as well.

Teacher's Note:
1. It is also a drying agent for gases (except NH₃ and H₂S).
2. Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O.

Answer: (a) (i), (ii) and (iv)

Explanation:
1. A basic flux is a basic oxide (or one that gives it) that removes acidic gangue such as SiO₂.
2. CaCO₃ (gives CaO on heating), CaO and MgO are basic fluxes, while SiO₂ is an acidic flux.

Teacher's Note:
1. Acidic gangue needs a basic flux; basic gangue needs an acidic flux.
2. CaO + SiO₂ → CaSiO₃ (slag).

Answer: (b) in the presence of air

Explanation:
1. As the passage says, roasting is done in the presence of air or oxygen.
2. The oxygen converts the sulphide into the oxide and SO₂.

Teacher's Note:
1. 2ZnS + 3O₂ → 2ZnO + 2SO₂.
2. Calcination is done in little or no air.

Answer: (a) Na

Explanation:
1. Only metals above hydrogen in the reactivity series displace hydrogen from acids.
2. Sodium is a metal; S, P and Si are non-metals or metalloids, which do not.

Teacher's Note:
1. Metals are electropositive and lose electrons easily.
2. 2Na + 2HCl → 2NaCl + H₂.

Answer: (b) are good conductors of heat

Explanation:
1. Good heat conductors transfer heat quickly from the flame to the food or water.
2. Copper and aluminium conduct heat well and have fairly high melting points.

Teacher's Note:
1. Silver is the best conductor but is costly.
2. Steel pans are given a copper base for the same reason.

Answer: (b) they are very unreactive and do not react with oxygen, water or acids

Explanation:
1. These metals are at the bottom of the reactivity series.
2. They are not attacked by air or moisture, so they stay uncombined.

Teacher's Note:
1. Only aqua regia dissolves gold.
2. They are called noble metals.

Answer: (b) CO and H₂O

Explanation:
1. Carbon monoxide and water neither react with acids nor with bases to form salts, so they are neutral.
2. CO₂ and SO₂ are acidic, Na₂O and CaO are basic and Al₂O₃ and ZnO are amphoteric.

Teacher's Note:
1. Other neutral oxides are N₂O and NO.
2. Learn all four types of oxides.

Answer: (c) by showing that they dissolve in water or acids to form bases or salts, turning red litmus blue

Explanation:
1. Soluble metal oxides such as Na₂O and CaO form alkalies with water that turn red litmus blue.
2. Metal oxides also react with acids to give a salt and water.

Teacher's Note:
1. CaO + H₂O → Ca(OH)₂.
2. Metal oxides + acid → salt + water.

Answer: (b) ZnO and SO₂; CaO and CO₂

Explanation:
1. Roasting ZnS in air: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
2. Calcining limestone: CaCO₃ → CaO + CO₂.

Teacher's Note:
1. Roasting uses air; calcination does not.
2. Both give oxides.

Answer: (a) (i) and (iii)

Explanation:
1. Iron is less reactive than zinc and cannot displace it, so (i) is not possible.
2. Copper is below hydrogen and does not react with dilute acid, so (iii) is not possible.
3. (ii) and (iv) are possible because Cu is more reactive than Ag and Zn is more reactive than Cu.

Teacher's Note:
1. Check the reactivity series for each displacement.
2. The more reactive metal must be the free metal.

Answer: (d) it has a very high melting point

Explanation:
1. The filament becomes white hot, so the metal must not melt.
2. Tungsten has a very high melting point (about 3380 °C).

Teacher's Note:
1. Alloys like solder have low melting points and are used for fuses.
2. Tungsten is also ductile.

Answer: (d) they have free (delocalised) electrons that can move easily

Explanation:
1. In a metal the outer electrons are not tied to any atom but form a sea of free electrons.
2. These carry charge and heat energy through the metal quickly.

Teacher's Note:
1. Silver and copper are the best conductors.
2. Non-metals have no free electrons.

Answer: (b) it has properties of both metals and non-metals

Explanation:
1. Metalloids such as Ge and Si show some properties of metals (lustre) and some of non-metals (brittle and poor conductors, semiconductors).
2. So they are in between metals and non-metals.

Teacher's Note:
1. Other metalloids: B, Si, As, Sb.
2. They lie along the zig-zag line of the periodic table.

Answer: (a) mercury; sodium; silver

Explanation:
1. Mercury is the only liquid metal at room temperature.
2. Sodium is soft and easily cut with a knife; silver is the best conductor of heat and electricity.

Teacher's Note:
1. Lead is a poor conductor of heat.
2. Alkali metals are soft.

Answer: (d) iron, chromium, nickel and carbon, with resistance to rusting as the property of chromium

Explanation:
1. Stainless steel is made from iron, chromium, nickel and a little carbon.
2. The chromium gives the corrosion resistance.

Teacher's Note:
1. Bronze is copper and tin.
2. An amalgam has mercury as one component.

Answer: (d) metals form positive ions and basic oxides, non-metals form negative ions or covalent compounds and acidic oxides

Explanation:
1. Metals lose electrons to form cations and their oxides are basic.
2. Non-metals gain or share electrons and their oxides are acidic, and they do not displace hydrogen from acids.

Teacher's Note:
1. Some metals form amphoteric oxides.
2. This is the basis of the classification.