What is the $pH$ value of a basic aqueous solution?

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.

How is an aqueous solution with $pH = 2$ compared to an aqueous solution with $pH = 4$?

Which of the following gives the correct increasing order of acidic strength?

What happens when $CO_2$ is passed through lime water in limited amount?

Salt $A$,commonly used in bakery products,on heating gets converted into another salt $B$,which itself is used for the removal of hardness of water,and a gas $C$ is evolved. The gas $C$,when passed through lime water,turns it milky. Identify $A$,$B$,and $C$.