In which form do $H^{+}$ (hydrogen) ions exist in water?

What is the $pH$ value of a basic aqueous solution?

$(a)$ What will you observe when dilute hydrochloric acid is added to a small amount of copper oxide in a beaker?
$(b)$ Aqueous solution of $HCl$ shows acidic character. But the aqueous solution of glucose fails to do so. Why?

Which gas is released when acid reacts with metal?

Match the important chemicals given in Column $(A)$ with the chemical formulae given in Column $(B)$.

Column $(A)$	Column $(B)$
$(a)$ Plaster of Paris	$(i)$ $Ca(OH)_{2}$
$(b)$ Gypsum	$(ii)$ $CaSO_{4} \cdot 1/2 H_{2}O$
$(c)$ Bleaching Powder	$(iii)$ $CaSO_{4} \cdot 2H_{2}O$
$(d)$ Slaked Lime	$(iv)$ $CaOCl_{2}$

Which of the following metals reacts with sodium hydroxide to produce a salt and $H_2$ gas?