Science M.C.Q. [I MARKS]

during the rusting of iron or iron metal combines slowly with the oxygen of air in the presence of water moisture to form a compound called 'iron oxide'. This iron oxide is rust the reaction of iron metal with oxygen in the presence of water. Therefore, oxide of iron rust is corrosion, it is a 'chemical reaction'.

Sodium reacts vigorously with oxygen and water, giving off a lot of heat so, it is stored in kerosene. Phosphorus catches fire on exposure to air and hence, stored in water. Iron reacts with steam.

during the rusting of iron or iron metal combines slowly with the oxygen of air in the presence of water moisture to form a compound called iron oxide. This iron oxide is rust the reaction of iron metal with oxygen in the presence of water. Therefore, oxide of iron rust is corrosion, it is a chemical reaction.

A substance which cannot be broken down into two or more simpler substances by chemical reaction is called an element. The smallest particle of an element is called atom. An element is a substance which is made up of only one kind of atoms. The atoms of an element remain unaffected by the physical changes in the element. Thus, an atom of liquid sulphur or vapour forms of sulphur would be same as that of solid sulphur.

Gold being less reactive than hydrogen is placed below hydrogen in reactivity series. It cannot produce hydrogen gas on reaction with acids.

Potassium reacts with water to potassium hydroxide and hydrogen gas. The reaction potassium with water is highly exothermic in nature. It produces a lot of heat energy and this heat energy can cause the hydrogen gas produced during the reaction, to catch fire. In order to keep it safe potassium is stored in kerosene.

Zinc sulphate solution and calcium cannot undergo displacement reaction.
This is because zinc is more reactive than iron. Hence, iron cannot displace zinc from zinc sulphate solution.

The less reactive metals like copper, silver and gold do not react with dilute hydrochloric acid to produce hydrogen gas.

Metal oxides are reduced to metals.

Calcium is more reactive than magnesium. Hence, Mg can be replaced from its salt by calcium.

Silver is least reactive and is placed below all these metals in reactivity series of metals.

The reactivity of silver is so low that it doesn’t react even with steam.

The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling.

Sodium has less density, hence it is soft and can be cut even with a knife.