What is the $H_{3}O^{+}$ ion called?

$A$ substance $X$, which is an oxide of a group $2$ element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify $X$ and write the chemical reactions involved.

Write true or false for the following statement:
Mixing an acid or base with water results in an increase in the concentration of ions $(H_{3}O^{+} / OH^{-})$ per unit volume.

While diluting an acid,why is it recommended that the acid should be added to water and not water to the acid?

What is formed by the reaction of a non-metal oxide with a base?

$(a)$ $A$ 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.