$A$ mixture of equal amounts of $H_2$ and $Cl_2$ gases in a gas jar produces white fumes in the absence of sunlight. What are these white fumes?

What is used as a catalyst in the production of sulfuric acid by the contact process?

What is the percentage of $H_{2}SO_{4}$ in concentrated $H_{2}SO_{4}$ (in $\%$)?

$(a)$ Why does calcium start floating when added to water?
$(b)$ Most metals do not release hydrogen gas when reacting with nitric acid. Why?
$(c)$ Write the chemical equation for the reaction of iron with steam. Name the compound of iron obtained.

State whether the following statement is true or false:
The elements or compounds,which occur naturally in the earth's crust,are known as minerals.

Heating of carbonate ores in the absence of air to convert them into oxides is known as: