K, L and M are beakers containing three different solutions: [Beaker K: Aqueous acetic acid, Beaker L: Sodium chloride solution, Beaker M: Distilled water]. Name the beaker which:
(a) contains only ions.
(b) contains only molecules.
(c) has pH less than 7. 
Give one relevant observation for the following:
(a) Sodium hydroxide is added dropwise to Calcium nitrate solution.
(b) Dilute Hydrochloric acid is added to Iron (II) sulphide.
(c) An amphoteric metal is added to hot concentrated alkali.