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

Mention the range of $pH$ value for identification of a base.

If $[H_3O^+] = 10^{-6} \ M$ in an aqueous solution,what is the $pH$ of the solution?

$(a)$ $A$ salt is produced by the reaction between an acid and a base. Identify the acid and the base from which the following salts have been formed:
$(i)$ $Na_{2}SO_{4}$
$(ii)$ $NH_{4}Cl$
$(iii)$ $KNO_{3}$
$(iv)$ $NaCl$

Which of the following is acidic in nature?

Write balanced chemical equations for the following:
$(i)$ Bleaching powder is kept open in air.
$(ii)$ Blue crystals of copper sulphate are heated.
$(iii)$ Chlorine gas is passed through dry slaked lime.