If the concentration of hydronium ions in an aqueous solution is $[H_3O^+] = 1 \; M$,what is the $pH$ of the solution?

What is the approximate $pH$ value for a solution,if $pH$ paper turns pink when dipped into it?

What is formed when an acid reacts with a base?

$Na_{2}CO_{3} \cdot 10H_{2}O$ and $Na_{2}CO_{3}$ are two chemical compounds. Write their chemical names. Explain the significance of $10H_{2}O$ and mention the term used for water molecules attached to a salt.

Dry hydrogen chloride gas does not turn blue litmus red whereas hydrochloric acid does. Give one reason.

Which enzyme becomes active in the stomach during a low $pH$ value?