Which scientist introduced the $pH$ scale?

$A$ 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.

Which gas is evolved when dilute hydrochloric acid reacts with zinc? Write the molecular formula of this gas.

Which among the following is not a base?

Give reasons for the following:
$(a)$ Aqueous solution of an acid conducts electricity.

The chemical formulas for Gypsum and Plaster of Paris are,respectively: