Write balanced chemical equations for the following:
$(i)$ Carbon dioxide gas is passed through lime water.
$(ii)$ $NaOH$ solution is heated with zinc granules.

$A$ solution of a substance '$X$' is used for testing carbon dioxide. Identify '$X$'. What will be its reaction with carbon dioxide? Write a balanced equation for the reaction.

$A$ 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?

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
$(i)$ It is an endothermic reaction
$(ii)$ It is an exothermic reaction
$(iii)$ The $pH$ of the resulting solution will be more than seven
$(iv)$ The $pH$ of the resulting solution will be less than seven

State one basic difference between a physical change and a chemical change.

What is the colour of $FeSO_{4} \cdot 7H_{2}O$ crystals? How does this colour change upon heating? Give the balanced chemical equation for the change.