CBSE Class 10 Science 2020 · Paper 31(B) · Question 25(a)

(a) Hydrogen gas (${\text{H}}_2$) is liberated. Test: when a burning candle or matchstick is brought near the gas (for example, near a soap bubble filled with it), the gas burns with a pop sound. (b) With $\text{HCl}$: zinc reacts to form zinc chloride and hydrogen gas, $\text{Zn}+2\text{HCl}⟶{\text{ZnCl}}_2+{\text{H}}_2\uparrow$; the salt is zinc chloride. With $\text{NaOH}$ (on warming): zinc reacts to form sodium zincate and hydrogen gas, $\text{Zn}+2\text{NaOH}⟶{\text{Na}}_2{\text{ZnO}}_2+{\text{H}}_2\uparrow$; the salt is sodium zincate. (c) Acid: hydrochloric acid ($\text{HCl}$); base: ammonium hydroxide (${\text{NH}}_4\text{OH}$). Ammonium chloride is the salt of a strong acid and a weak base, so it is acidic in nature and its pH is less than $7$.