What will be the $pH$ of an aqueous solution of $NH_{4}Cl$?

$15 \, mL$ 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?

Whose acid-base theory can be applied to aqueous and non-aqueous solutions?

What is the $H_{3}O^{+}$ ion called?

In one of the industrial processes used for the manufacture of sodium hydroxide,a gas $X$ is formed as a by-product. The gas $X$ reacts with lime water to give a compound $Y$,which is used as a bleaching agent in the chemical industry. Identify $X$ and $Y$ and provide the chemical equations for the reactions involved.

Name the gas which is liberated when an acid reacts with a metal. Illustrate with an example. How will you test the presence of this gas?