(a)(i) Oxide of non-metals which dissolve in water to form acidic solution.
(ii) 1. Acidic oxides:- SO${}_2$/CO${}_2$/NO${}_2$, etc.
2. Basic oxides:- CaO/Na${}_2$O/K${}_2$O, etc.
3. Amphoteric oxides:- Al${}_2$O${}_3$/ZnO/PbO, etc.
4. Neutral oxides:- CO/N${}_2$O, etc.

(b)(i) Heat of combustion is the heat change when one mole of a substance is completely burnt in oxygen or burnt in excess oxygen
(ii) Heat of neutralization is the heat change when one mole of water is produced as a result of a reaction between an acid and alkali in dilLte solution or the heat change when one mole of H+ from an acid reacts with one mole of OH${}^{-}$ from an alkali to form one mole of H${}_2$O.
(ii)1. C${}_{(g)}$ + O${}_{2(g)}$ $\to$ CO${}_{2(g)}$
2. HaOH${}_{(aq)}$ + HCl${}_{(aq)}$ $\to$ NaCI + H${}_2$O${}_{(l)}$ $\mathrm{\Delta }$ Hn${}^o$
3. Molar mass of C${}_4$H${}_{10}$ = 12 x 4 + 1 x 10
= 48 + 10 = 58g mol${}^{-1}$ .
58g of C${}_4$H${}_{10}$ = 5877kJ mol${}^{-1}$
14.5 of C${}_4$H${}_{10}$ = $\frac{5877\times 14}{58}$ kJ mol${}^{-1}$
= + 1469.25 kJ.

(c)(i) Rhombic
Monoclinic

Rhombic	Monoclinic
Yellow translucent crystal	Transparent amber crystal
Stable at temperature below 96°C	Unstable at temperature below 96°C
Higher density than monoclinic	Lower density than rhombic
Lower melting point	Higher melting point
Octahedral shaped	Needle shaped.

(d)(i)(a) They are monoatomic gases
(b) They are chemically unreactive
(c) Have low melting/boiling point.
(ii) He — filling balloons. Ar — arc welding.