Which of the following phenomena occur, when a small amount of acid is added to water?
(i) Ionisation
(ii) Neutralisation
(iii) Dilution
(iv) Salt formation
(i) and (ii)
(i) and (iii)
(ii) and (iii)
(ii) and (iv)
Steps: Adding acid to water causes ionisation (HCl → H⁺ + Cl⁻) and dilution (the acid concentration decreases). Neutralisation and salt formation require a base present.