Q.(a)

(a) Paint is a solid-dispersed-in-liquid sol, froth of air is a gas-dispersed-in-liquid foam, and a catalytic poison (e.g. arsenic) deactivates a catalyst by blocking its active sites. (b) A buffer resists pH change, and for this equal-concentration propionic-acid/propionate buffer $pH=pK_a\approx4.74$.

(a)(i) Dispersed phase and dispersion medium:

(a)(ii) Catalytic poison: A catalytic poison is a substance which, even in a small amount, gets preferentially adsorbed on the active sites of a (usually solid/heterogeneous) catalyst, blocking those sites and thereby reducing or completely destroying the catalyst's activity. Example: in the Contact process for manufacturing sulfuric acid, traces of arsenic compounds (e.g. $As_2O_3$) present in the sulfur dioxide feed gas act as a catalytic poison for the platinum catalyst used to oxidise $SO_2$ to $SO_3$, permanently deactivating it (which is why platinum has largely been replaced by the less easily poisoned vanadium pentoxide, $V_2O_5$, catalyst in modern plants). Another classic example is carbon monoxide poisoning the iron catalyst used in the Haber process for ammonia synthesis.

(b)(i) Buffer solution: A buffer solution is one that resists a (large) change in its pH when a small amount of a strong acid or strong base is added to it, or on moderate dilution. An acidic buffer is made from a weak acid together with a salt of that weak acid with a strong base (e.g. $CH_3COOH + CH_3COONa$, or here propionic acid + sodium propionate), while a basic buffer is made from a weak base together with a salt of that weak base with a strong acid (e.g. $NH_4OH + NH_4Cl$).

(b)(ii) pH of the propionic acid/sodium propionate buffer:

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