CBSE Class 10 Science Metals and Non Metals MCQs Set 09

Answer: (d) Hg

Explanation:
1. All metals are solids at room temperature except mercury.
2. Mercury (Hg) is the only metal that is liquid at room temperature.

Teacher's Note:
1. Remember the one liquid metal and the one liquid non-metal.
2. Gallium and caesium melt only on warming, near body temperature.

Answer: (d) carbon

Explanation:
1. Aluminium, silver and gold are metals and are highly malleable.
2. Carbon is a non-metal and is brittle (non-malleable), so it is the least malleable.

Teacher's Note:
1. Non-metals are brittle and break on hammering.
2. Compare each option with the word metal or non-metal first.

Answer: (d) Bromine

Explanation:
1. Aluminium and mercury are metals, so they are not non-metals.
2. Iodine is a solid at 25°C. Bromine is the only liquid non-metal.

Teacher's Note:
1. First remove the metals from the list.
2. Bromine is a volatile reddish-brown liquid.

Answer: (b) Copper

Explanation:
1. Magnesium burns with a dazzling white flame and lithium and sodium burn vigorously.
2. Copper does not burn. It only gets a black coating of copper(II) oxide.

Teacher's Note:
1. Copper becomes coated with black CuO on heating.
2. Silver and gold do not react with oxygen even on strong heating.

Answer: (a) Graphite

Explanation:
1. Phosphorus, hydrogen and bromine do not conduct electricity.
2. Graphite has free electrons and conducts electricity.

Teacher's Note:
1. Graphite is used as electrodes in cells.
2. It is an allotrope of carbon.

Answer: (c) Fe₃O₄

Explanation:
1. Iron reacts with steam to form the mixed oxide Fe₃O₄ and hydrogen.
2. The equation is 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

Teacher's Note:
1. Iron does not react with cold or hot water, only with steam.
2. The oxide formed is magnetic black iron oxide.

Answer: (d) AgNO₃ solution and copper metal.

Explanation:
1. A metal displaces another from its salt solution only if it is more reactive.
2. Copper is more reactive than silver, so it displaces silver from AgNO₃. In the other pairs the metal added is less reactive than the metal in the salt.

Teacher's Note:
1. Compare the positions in the reactivity series.
2. The displaced metal must be lower than the metal added.

Answer: (d) CuSO₄ + Fe

Explanation:
1. Iron is less reactive than magnesium and zinc, and lead is less reactive than magnesium, so (a), (b) and (c) show no reaction.
2. Iron is more reactive than copper, so Fe + CuSO₄ → FeSO₄ + Cu takes place.

Teacher's Note:
1. The added metal must be higher in the reactivity series.
2. Iron displaces copper but not zinc or magnesium.

Answer: (c) NaAlO₂

Explanation:
1. Aluminium oxide is amphoteric, so it reacts with sodium hydroxide.
2. The product is sodium aluminate, NaAlO₂, and water: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O.

Teacher's Note:
1. Name the salt as sodium aluminate.
2. Here Al2O3 reacts with a base, so it behaves like an acidic oxide.

Answer: (a) gold

Explanation:
1. Sodium is very reactive and is never found free, and silver and copper are usually found as compounds also.
2. Gold is the least reactive of these, so it is always found in the free state.

Teacher's Note:
1. Least reactive metals occur in the native state.
2. Gold and platinum are noble metals.

Answer: (b) beaker B

Explanation:
1. Copper is less reactive than zinc and iron, so it does not displace them from beakers A and C.
2. Copper is more reactive than silver and displaces it from silver sulphate, forming blue copper(II) sulphate solution in beaker B.

Teacher's Note:
1. Blue solution indicates Cu2+ ions.
2. Copper displaces only the metals below it.

Answer: (b) alkaline

Explanation:
1. Magnesium oxide is a basic oxide.
2. It dissolves in water to form Mg(OH)₂, which makes the solution alkaline.

Teacher's Note:
1. Basic oxide in water gives alkali.
2. The solution turns red litmus blue.

Answer: (d) Beaker 1: KOH and H₂; Beaker 2: No reaction takes place

Explanation:
1. Potassium reacts violently with cold water to form potassium hydroxide and hydrogen: 2K + 2H₂O → 2KOH + H₂.
2. Silver does not react with water, so nothing happens in Beaker 2.

Teacher's Note:
1. Highly reactive metals give a hydroxide and hydrogen with water.
2. Silver, gold and copper do not react with water.

Answer: (d) Metal ions gain electrons to become neutral metal atoms.

Explanation:
1. The negative electrode is the cathode, where reduction takes place.
2. Metal ions from the solution gain electrons and are deposited as neutral metal atoms: Cu²⁺ + 2e⁻ → Cu.

Teacher's Note:
1. Reduction takes place at the cathode.
2. Pure metal gets deposited on the cathode.

Answer: (d) Y is a non-metal and Z is a metal

Explanation:
1. X (2, 8) has a complete octet, so it is a noble gas.
2. Y (2, 8, 7) needs one more electron and is a non-metal (chlorine), while Z (2, 8, 2) has two valence electrons and is a metal (magnesium).

Teacher's Note:
1. Metals have 1 to 3 valence electrons.
2. Non-metals have 4 to 8 valence electrons.

Answer: (b) (III) and (IV)

Explanation:
1. Ionic compounds are formed by transfer, not sharing, of electrons, so (I) is wrong.
2. They do not conduct in the solid state, so (II) is wrong. They are soluble in water and have high melting points, so (III) and (IV) are correct.

Teacher's Note:
1. Check each statement separately.
2. Ionic compounds conduct only when molten or dissolved.

Answer: (d) 2, 8

Explanation:
1. A sodium atom has the configuration 2, 8, 1.
2. It loses one electron to form Na⁺, so the ion has the configuration 2, 8.

Teacher's Note:
1. Remove the outermost electron.
2. The ion has the same configuration as neon.

Answer: (a) 18

Explanation:
1. A neutral atom of A has 19 electrons.
2. The ion A⁺ has lost one electron, so it has 18 electrons.

Teacher's Note:
1. A positive charge means electrons lost.
2. Protons never change in ion formation.

Answer: (d) (i) and (ii)

Explanation:
1. Highly reactive metals such as sodium and calcium cannot be reduced by carbon.
2. They are obtained by electrolysis of their molten chlorides, so the answer is (i) and (ii).

Teacher's Note:
1. Reactive metals at the top are extracted by electrolysis.
2. Fe and Cu are reduced by heating with carbon or by simple heating.

Answer: (b) Roasting

Explanation:
1. Heating a sulphide ore strongly in excess air is called roasting.
2. For example, 2ZnS + 3O₂ → 2ZnO + 2SO₂.

Teacher's Note:
1. Roasting needs plenty of air.
2. The gas given off from sulphides is SO2.

Answer: (c) Calamine – Aluminium

Explanation:
1. Chalcocite is an ore of copper, magnetite is an ore of iron and galena is an ore of lead.
2. Calamine is a carbonate ore of zinc, not aluminium, so (c) is incorrect.

Teacher's Note:
1. Calamine is ZnCO3.
2. The ore of aluminium is bauxite.

Answer: (c) Gangue

Explanation:
1. Ores mined from the earth contain impurities such as sand, soil and rocks.
2. These impurities are called gangue (or matrix).

Teacher's Note:
1. Gangue is the unwanted material in the ore.
2. Slag is formed when a flux combines with the gangue.

Answer: (c) (iii) and (iv)

Explanation:
1. These metals have a very high affinity for oxygen, so carbon has less affinity for oxygen than they do.
2. Carbon is therefore a weaker reducing agent than these metals and cannot remove oxygen from their oxides.

Teacher's Note:
1. A reducing agent must have a greater affinity for oxygen.
2. Hence electrolysis is used for them.

Answer: (d) Iron

Explanation:
1. Iron(III) oxide Fe₂O₃ does not react with water, and iron forms two chlorides, FeCl₂ and FeCl₃.
2. Aluminium forms only AlCl₃ and zinc and copper do not form M₂O₃ with two such chlorides.

Teacher's Note:
1. A metal with two valencies forms two chlorides.
2. Iron shows +2 and +3.

Answer: (a) Ni and Cr

Explanation:
1. Stainless steel is an alloy of iron with nickel and chromium and a little carbon.
2. Nickel and chromium make it resistant to rusting.

Teacher's Note:
1. Stainless steel does not rust.
2. Remember Fe, Ni, Cr.

Answer: (a) Pb and Sn

Explanation:
1. Solder is an alloy of lead and tin.
2. It has a low melting point, so it is used for welding electrical wires.

Teacher's Note:
1. Solder: lead + tin.
2. Low melting point is the useful feature.

Answer: (b) hydrated ferric oxide

Explanation:
1. Rust forms when iron reacts with oxygen and moisture.
2. It is hydrated iron(III) oxide, Fe₂O₃.xH₂O.

Teacher's Note:
1. Rust is a hydrated oxide of iron.
2. The ferric state is Fe3+.

Answer: (b) Sodium, Potassium

Explanation:
1. Sodium and potassium react so vigorously with oxygen and moisture that they can catch fire in the open.
2. They are therefore stored under kerosene oil.

Teacher's Note:
1. Phosphorus (white) is stored under water.
2. Na, K and Li are kept in oil.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Metals in their pure state have a shining surface, which is called metallic lustre.
2. Both statements are true and the reason explains the assertion.

Teacher's Note:
1. Lustre means a shining surface.
2. Tarnishing hides lustre.

Answer: (d) A is false, but R is true.

Explanation:
1. Food cans are coated with tin and not with zinc, so A is false.
2. Zinc is above tin in the reactivity series, so R is true. Zinc would react with acids in food.

Teacher's Note:
1. Check the assertion carefully, it reverses the fact.
2. Tin is less reactive and safer for food.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Copper does not react with cold water, hot water or steam, so the tank is not damaged.
2. Steel contains iron, which reacts with steam, so both statements are true and R explains A.

Teacher's Note:
1. Iron reacts with steam, copper does not.
2. Hot water tanks must not corrode.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Copper is a good conductor of electricity, so it is used for wires and A is true.
2. Non-metals are bad conductors, so R is true, but it does not explain why copper is used.

Teacher's Note:
1. A good conductor is chosen for wires.
2. The reason should talk about copper.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Silicon shows properties of both metals and non-metals, so it is a metalloid and A is true.
2. Silicon is used as a semiconductor, so R is true, but being used as a semiconductor is not the reason it is classified as a metalloid.

Teacher's Note:
1. Metalloids: B, Si, Ge, As, Sb, Te.
2. They are intermediate in properties.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. In an ionic compound the ions are held strongly in a regular three-dimensional crystal lattice.
2. This closely packed structure makes ionic compounds solids, so R explains A.

Teacher's Note:
1. Strong attraction gives a rigid lattice.
2. The lattice also explains the high melting point.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Zinc oxide reacts with acids as well as with bases to form salt and water.
2. That is the definition of an amphoteric oxide, so R explains A.

Teacher's Note:
1. Al2O3 and ZnO are the usual amphoteric oxides.
2. Amphoteric means acts as acid or base.

Answer: (c) A is true, but R is false.

Explanation:
1. Zinc is in the middle of the reactivity series, so its oxide can be reduced by carbon: ZnO + C → Zn + CO, and A is true.
2. Carbon has a greater affinity for oxygen than zinc at high temperature, so it is more reactive here. R is false.

Teacher's Note:
1. Reducing agent must be more reactive towards oxygen.
2. Carbon cannot reduce Na2O or Al2O3.