Which solution will be basic?

$(a)$ $A$ solution of a substance $'X'$ is used for testing carbon dioxide. Write the equation of the reaction of $'X'$ with carbon dioxide.
$(b)$ How is $'X'$ obtained? Write the chemical equation.

Which substance is added to the soil to neutralize acidic soil?

In an acidic aqueous solution,the value of $[H_3O^+]$ is $.......$.

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

If the $pH$ of the aqueous solutions $A, B, C$ and $D$ are $1.9, 2.5, 2.1$ and $3.0$ respectively,then what will be the order of acidity?