Class 10 Science Chapter 3 MCQ

Hydrogen (H) is the non-metal element which loses electrons to form positive ions, hydrogen ions (H+).

Electrical wires have a coating of an insulting material called PVC (Polyvinylchloride). PVC is a polymer and bad conductor of electricity. It is the most common insulating material used to insulate electrical conductors from electric charge thus preventing human contact with live electricity. Graphite is good conductor of electricity. Hence it cannot be used as insulating material. Sulphur, although is a bad conductor of electricity, but is brittle in nature. So, cannot be used as insulating material.

Zinc amalgam contains mercury as one of its constituents. An alloy of mercury with another metal is called amalgam. Almost all metals except iron, platinum, tungsten, and tantalum can form amalgams with mercury. Amalgams of silver and mercury are important in dentistry. Amalgams of gold and mercury are used in the extraction of gold from its ore. Note: Stainless steel: An alloy of Fe and C, Alnico: An alloy of Al, Ni and Co, and Solder: An alloy of Pb and Sn.

Magnesium metal reacts with cold water to form magnesium oxide and evolves hydrogen gas is an incorrect statement. Magnesium when reacts with water gives magnesium hydroxide and hydrogen gas. Reaction of metals and water generally produce hydrogen gas and their respective hydroxide. For example, sodium metal reacts with water to produce sodium hydroxide and liberates hydrogen gas.

Gallium and cesium metals also have low melting points (of 30°C and 28°C respectively). The melting points of gallium and cesium metals are so low that they start melting in hand (by the heat of our body).

The metals which have high densities, we mean that metals are heavy substances. For example, the density of iron is 7.8 g/cm3 which is quite high. So, iron metal is a heavy substance. There are, however, some exceptions. For example, sodium and potassium metals have low densities (of 0.97 g/cm3 and 0.86 g/cm3 respectively). They are very light metals.

Non-metals are brittle which means that non-metals break into pieces when hammered or stretched. For example, sulphur and phosphorus are solid non-metals which are non-malleable and non-ductile.

An electrolytic cell consists of positively charged anode and negatively charged cathode. Positively charged ions (cations) are deposited at negatively charged cathode. Negatively charged ions (anions) are deposited at positively charged anode.

Only one non-metal carbon (in the form of diamond) is very hard. In fact, diamond (which is an allotropic form of carbon) is the hardest natural substance known

Test tube C contains chemical mixture called aqua-regia. It is a mixture of concentrated HCl and concentrated HNO3 in the ratio of 3:1. Aqua-regia dissolves gold and platinum in it while hydrochloric acid and nitric acid do not.

Magnesium metal does not react with cold water. Magnesium reacts with hot water to form magnesium hydroxide and hydrogen: You can easily understand by this equation: Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g) Magnesium + Water (hot) → Magnesium hydroxide + Hydrogen

Alloying elements enhance the structure and properties such as durability, strength and toughness of the metal. It makes them corrosion resistant. Stainless steel is an alloy of iron, nickel and chromium.

Silver articles turn black after prolonged exposure to air due to the reaction of sulphur present in air. Silver reacts with sulphur to form dark grey to black silver sulphide.

Here, all the statements are correct. Hence, your answer will be option [D].

Nitrogen is an inert gaseous non-metal whose presence in air reduces the rate of combustion and makes it safe.

In solid state, ions in ionic compounds are not free to move. Thus, such compounds do not show electrical conductivity in solid state. Whereas, in molten state, ions are free to move and hence conduct electricity.

Here, all the statements are correct. Hence, your answer will be option [D].

Aqua-regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua-regia being a very strong acid dissolves gold in it.

Pure gold, known as 24 carat gold, is very soft. It is, therefore, not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. Generally, in India, 22 carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either copper or silver.

Aqua regia, (Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.

Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire. You can easily understand by this equation: 2K(s) + 2H2O(l) → 2KOH(aq) + H2 (g) + heat energy 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) + heat energy

When steam is passed over iron for a long time, it gives iron oxide (Fe3O4) and hydrogen gas. You can easily understand by this equation: 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Na (sodium) and Ca(calcium) react with water vigorously. Mg (Magnesium) reacts with water less vigorously than that of calcium and sodium. Fe (Iron), on the other hand, does not react with cold as well as hot water instantly. But when the iron is kept in contact with water for a long time, rusting of iron happens.

The ability of metals to be drawn into thin wire is called ductility. It is one such property of metals that is used to make wires from metals. Metals such as copper have high ductility and thus can be drawn into long and thin wires without breaking.

Metals generally do not show dullness. Metals such as gold and silver usually are shiny rather than dull.