Class 10 Science Chapter 3 MCQ

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.

Graphite is a good conductor of electricity and heat. Graphite has weak intermolecular forces between its layers. Hence it has de-localised electrons. As electrons are free to move through its structure, it conducts heat and electricity well.

The major non-metals in the earth’s crust in the decreasing order of their abundance are: Oxygen, Silicon, Phosphorus and Sulphur.

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

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).

Non-metals have low melting points and boiling points. But diamond is an exception. Diamond is a non-metal which has a very high melting point and boiling point (just like metals).

A solution of sulphur dioxide in water turns blue litmus to red. This shows that sulphur dioxide is acidic in nature.

Iodine is a non-metal that is lustrous. Graphite is another non-metal that is shiny and lustrous.

Sodium and calcium are very reactive metals and are placed towards the top of the reactivity series. These are produced by the electrolysis of their molten chlorides. The metal ions are deposited at negatively charged cathode and chlorine is deposited at positively charged anode.

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

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

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].

Gold (Au) and silver (Ag) are not reactive or very less reactive. These metals are called noble metals. Thus, these are placed at the bottom of the reactivity series. Since gold and silver are least reactive of all the metals, these are found in free state in nature.

Some metals are chemically very reactive whereas others are less reactive or unreactive. For example, potassium and sodium react very, very rapidly with cold water, so they are very reactive metals. Zinc and iron react only with steam, so they are less reactive metals. On the other hand, copper and silver do not react even with steam, so they are quite unreactive metals. Silver and gold metals also do not react with dilute acids.

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

Copper metal is more reactive than silver metal (Ag), so a displacement reaction will take place between AgNO3 solution and copper metal. In option A: Copper metal is less reactive than sodium metal (Na), so no displacement reaction will occur between NaCl solution and copper metal. In option B: Aluminium metal is less reactive than magnesium metal (Mg), so no displacement reaction will take place between MgCl2 solution and Aluminium metal. In option C: Silver metal is less reactive than iron metal (Fe), so no displacement reaction will occur between FeSO4 solution and silver metal.

If a metal is below hydrogen in the activity series, then it will not displace hydrogen from water and acids, that is, it will not react with water and acids to produce hydrogen gas. We should remember the reactivity series of metals to decide whether a particular displacement reaction will take place or not.

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.