In a basic aqueous solution,if the concentration of $[OH^-]$ decreases,what happens to the $pH$?

Which of the following statements is correct about an aqueous solution of an acid and of a base?
$(i)$ Higher the $pH$,stronger the acid
$(ii)$ Higher the $pH$,weaker the acid
$(iii)$ Lower the $pH$,stronger the base
$(iv)$ Lower the $pH$,weaker the base

How is an aqueous solution with $pH = 2$ compared to an aqueous solution with $pH = 4$?

Complete and balance the following chemical equations:
$(a)$ $Ca(OH)_{2} + Cl_{2} \longrightarrow$
$(b)$ $CaSO_{4} \cdot 1/2 H_{2}O + H_{2}O \longrightarrow$
$(c)$ $Na_{2}CO_{3} \cdot 10H_{2}O \xrightarrow{\text{air}} \dots$

Common salt, besides being used in the kitchen, can also be used as the raw material for making:
$(i)$ Washing soda
$(ii)$ Bleaching powder
$(iii)$ Baking soda
$(iv)$ Slaked lime

Answer the following:
$(i)$ Why is Plaster of Paris written as $CaSO_{4} \cdot 1/2 H_{2}O$? How is it possible to have half a water molecule attached to $CaSO_{4}$?
$(ii)$ Why is sodium hydrogen carbonate an essential ingredient in antacids?
$(iii)$ When electricity is passed through an aqueous solution of sodium chloride,three products are obtained. Why is the process called chlor-alkali?