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

Which of the following statements is not correct?

$(a)$ Write the chemical name and chemical formula of washing soda.
$(b)$ How is it obtained from sodium chloride? Give equations of the reactions.
$(c)$ Why is it called a basic salt? Give any one of its uses.

Write balanced chemical equations for the following:
$(i)$ Carbon dioxide gas is passed through lime water.
$(ii)$ $NaOH$ solution is heated with zinc granules.

The aqueous solution having $pH \, 11$ is how many times more basic than an aqueous solution having $pH \, 8$?

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