(a) Dry HCl gas does not change the colour of dry litmus paper. Why?

(b) Is PbO₂ a base or not? Comment.

(c) Do basic solutions also have H⁺(aq.) ? Explain why are they basic by taking an example?

(a) The colour of litmus paper changes only in presence of ions like hydrogen [H⁺] or hydronium ions [H₃O⁺]. HCl can produce these ions only in the form of aqueous solution. Hence, dry HCl gas does not change the colour of dry litmus paper.

(b) A base reacts with an acid to form salt and water ONLY. The word ONLY is of importance in the definition of a base. Lead oxide reacts with hydrochloric acid to produce lead (II) chloride (a salt) and water, but the word "only" excludes it from the class of bases because chlorine is also produced.

PbO₂(s) + 4HCl(aq.) ⟶ PbCl₂(aq.) + Cl₂(g) + 2H₂O

Thus, PbO₂ is not a base.

(c) Yes, basic solutions have H⁺ ions, but the concentration of OH^- ions is more than the H⁺ ions which makes the solution basic in nature.

Example — Sodium hydroxide (NaOH). It has more OH^- ions than H⁺ ions, so it is basic in nature.