Which gas is highly soluble in water?

$A$ dry pellet of a common base $B$,when kept in open,absorbs moisture and turns sticky. The compound is also a by-product of the chlor-alkali process. Identify $B$. What type of reaction occurs when $B$ is treated with an acidic oxide? Write a balanced chemical equation for one such reaction.

Equal lengths of magnesium ribbon are taken in two test tubes $A$ and $B$. $H_{2}SO_{4}$ is added to test tube $A$ and $H_{2}CO_{3}$ in test tube $B$ in equal amounts.
$(a)$ Identify the test tube showing vigorous reaction.
$(b)$ Give reason to support your answer.
$(c)$ Name the gas liberated in both the test tubes. How will you prove its liberation?

Give suitable reasons for the following statements: An aqueous solution of sodium chloride is neutral,but an aqueous solution of sodium is basic.

What is the percentage of $H_{2}SO_{4}$ in concentrated $H_{2}SO_{4}$ (in $\%$)?

What is the percentage of $H_{2}SO_{4}$ in dilute sulfuric acid (in $\%$)?