State if the following statement is true or false. Correct the false statement. The principal gases of air are hydrogen and helium.

The given statement is incorrect. Air is a mixture of gases that primarily contains nitrogen 78 % and oxygen 21 % rest other gases are in trace amounts.

State if the following statement is true or false. Correct the false statement. Oxygen is collected by the downward displacement of water.

Oxygen is collected by the downward displacement of water because it is slightly heavier than air and slightly soluble in water and it will easily mix with air. If we use the downward displacement method, oxygen will collect over the liquid and it does not mix with air. Hence, the given statement is correct.

State if the following statement is true or false. Correct the false statement. A catalyst is a substance that alters the rate of a chemical reaction.

A catalyst can be defined as a substance that alters the rate of the reaction without being consumed by the reactant that is the catalyst does not undergo any change in the chemical reaction. It only provides a favourable condition or surface on which the reactants could react easily and effectively to give the desired products. Hence, the given statement is correct.

State if the following statement is true or false. Correct the false statement. The action of dilute sulphuric acid on marble chips produces carbon dioxide.

Marble chips are calcium carbonate so when dilute sulphuric acid is when poured over marble chips, it forms calcium sulphate and liberates carbon dioxide. Hence, the given statement is correct.