CBSE Class 10 Science Metals and Non-metals MCQs Set 13

Answer: (b) Gold. Gold can be beaten into extremely thin sheets, so it is the most malleable.

Teacher's Note:
1. Malleability means a metal can be beaten into sheets.
2. Gold and silver are the best examples.

Answer: (a) Mercury and bromine. Mercury is the only liquid metal and bromine the only liquid non-metal at room temperature.

Teacher's Note:
1. Gallium and caesium melt only slightly above room temperature.
2. Remember this pair for quick recall.

Answer: (c) Iodine. Iodine has a shining appearance even though it is a non-metal.

Teacher's Note:
1. Most non-metals are dull.
2. Graphite, a form of carbon, is a good conductor too.

Answer: (b) reacts vigorously with oxygen and moisture. Sodium is highly reactive and may catch fire in air.

Teacher's Note:
1. Potassium is stored the same way.
2. White phosphorus is stored under water.

Answer: (c) Mg. The order is Mg > Zn > Fe > Cu.

Teacher's Note:
1. The reactivity series is built from displacement and water or acid reactions.
2. Copper is the least reactive here.

Answer: (b) joining railway tracks. Aluminium reduces iron(III) oxide to molten iron, which welds the cracks.

Teacher's Note:
1. The reaction releases a very large amount of heat.
2. Fe₂O₃ + 2Al → Al₂O₃ + 2Fe.

Answer: (c) Al₂O₃. Al₂O₃ reacts with both acids and bases to give salt and water.

Teacher's Note:
1. ZnO is another common amphoteric oxide.
2. Na₂O and MgO are basic.

Answer: (b) 3 : 1. The mixture is 3 parts HCl to 1 part HNO₃ by volume.

Teacher's Note:
1. It is called royal water because it dissolves gold and platinum.
2. Neither acid alone can do so.

Answer: (b) HNO₃ is a strong oxidising agent and oxidises the H₂ to water. HNO₃ oxidises the hydrogen formed into water and is itself reduced to nitrogen oxides.

Teacher's Note:
1. Only magnesium and manganese give hydrogen with very dilute HNO₃.
2. This is an exception worth remembering.

Answer: (c) conduct electricity in the molten state. Ions become free to move in the molten state and in solution.

Teacher's Note:
1. In the solid state the ions are fixed in position.
2. Ionic compounds have high melting points.

Answer: (b) loses 2 electrons. Mg (2,8,2) loses two electrons to become Mg²⁺.

Teacher's Note:
1. Each chlorine atom gains one electron, so two chlorine atoms are needed.
2. This forms an ionic bond.

Answer: (b) impure copper. Impure copper dissolves at the anode and pure copper is deposited on the cathode.

Teacher's Note:
1. The electrolyte is acidified copper sulphate solution.
2. Impurities settle below the anode as anode mud.

Answer: (b) bauxite. Bauxite (Al₂O₃·2H₂O) is the main ore of aluminium.

Teacher's Note:
1. Haematite is the iron ore.
2. Cinnabar is the ore of mercury and galena of lead.

Answer: (b) in excess air. Sulphide ores are converted to oxides by heating strongly in excess air, e.g. 2ZnS + 3O₂ → 2ZnO + 2SO₂.

Teacher's Note:
1. Calcination is heating a carbonate ore in limited air.
2. Both processes give a metal oxide.

Answer: (b) ZnCO₃. ZnCO₃ → ZnO + CO₂ when heated in limited air.

Teacher's Note:
1. Calcination removes volatile impurities and moisture from carbonate ores.
2. The oxide is then reduced.

Answer: (b) electrolysis of molten alumina. Aluminium is too reactive to be reduced by carbon, so molten Al₂O₃ mixed with cryolite is electrolysed.

Teacher's Note:
1. Cryolite lowers the melting point and increases conductivity.
2. Metals above zinc in the series are extracted by electrolysis.

Answer: (b) basic copper carbonate. Copper reacts with moist CO₂ to form green basic copper carbonate.

Teacher's Note:
1. Silver turns black due to silver sulphide.
2. Iron forms brown rust.

Answer: (b) zinc. A layer of zinc protects iron from rusting, even if the layer is scratched.

Teacher's Note:
1. Zinc is more reactive and corrodes in preference to iron.
2. This is also called sacrificial protection.

Answer: (b) Cu and Zn. Brass contains copper and zinc.

Teacher's Note:
1. Bronze is Cu and Sn, solder is Pb and Sn.
2. Alloys have improved strength and resistance to corrosion.

Answer: (a) the solution turns from blue to pale green. Fe + CuSO₄ → FeSO₄ + Cu; green iron(II) sulphate forms and brown copper deposits on the nail.

Teacher's Note:
1. Iron is more reactive than copper.
2. This is a displacement reaction.

Answer: (c) blue. Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag; Cu²⁺ ions give a blue colour.

Teacher's Note:
1. Silver is deposited in shining crystals on the wire.
2. Copper is more reactive than silver.

Answer: (d) Copper. Copper is below hydrogen in the reactivity series.

Teacher's Note:
1. Metals above hydrogen displace it from acids.
2. Copper, silver and gold do not.

Answer: (c) Silver. Silver has the highest electrical conductivity of all metals.

Teacher's Note:
1. Copper is next and is used for wires due to its lower cost.
2. Lead and mercury are poor conductors.

Answer: (c) Sodium. 2Na + 2H₂O → 2NaOH + H₂; the heat can ignite the hydrogen.

Teacher's Note:
1. Magnesium reacts with hot water, and iron with steam.
2. Sodium and potassium react with cold water.

Answer: (b) Fe₃O₄ and H₂. 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

Teacher's Note:
1. The metal oxide, not hydroxide, is formed in this reaction.
2. The gas given out is hydrogen.

Answer: (b) graphite. Graphite has free electrons in its layered structure.

Teacher's Note:
1. Diamond is a poor conductor and the hardest natural substance.
2. Graphite is used as electrodes.

Answer: (a) hydrogen gas and sodium zincate. Zn + 2NaOH → Na₂ZnO₂ + H₂.

Teacher's Note:
1. This shows that some metals react with bases also.
2. Aluminium shows similar behaviour.

Answer: (a) Both A and R are true and R is the correct explanation of A. Kerosene keeps sodium away from air and water, so R explains A.

Teacher's Note:
1. Reaction with air can cause fire.
2. Hence it is cut and handled with care.

Answer: (a) Both A and R are true and R is the correct explanation of A. Good conduction of heat allows the food to cook quickly, so R explains A.

Teacher's Note:
1. Aluminium is also light and resists corrosion.
2. Its oxide layer protects the metal.