$pH + pOH = ?$

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
$(i)$ The temperature of the solution increases
$(ii)$ The temperature of the solution decreases
$(iii)$ The temperature of the solution remains the same
$(iv)$ Salt formation takes place

$15 \, mL$ of water and $10 \, mL$ of sulphuric acid are to be mixed in a beaker.
$(i)$ State the method that should be followed with reason.
$(ii)$ What is this process called?

The concentration of $H_{3}O^{+}$ in $1\,M\,H_{2}SO_{4}$ aqueous solution is $.......$ (in $,M$)

Write balanced chemical equations for the following:
$(a)$ Calcium carbonate reacts with hydrochloric acid.
$(b)$ Calcium oxychloride reacts with hydrochloric acid.
$(c)$ Sodium hydroxide reacts with zinc.

State whether the following statement is true or false:
When the $pH$ of rainwater is more than $5.6,$ it is called acid rain.