(a) X — CaCO${}_3$ Y — Ca(NO${}_3$)${}_2$

(b)i) 2NH${}_{3(g)}$ + 3CuO${}_{(s)}$ $\to$ 3Cu${}_{(s)}$ + 3H${}_2$O${}_{(g)}$ + N${}_{2(g)}$
(ii) *Explosion may occur. *Because ammonium dioxonitrate (Ill) is unstable and decomposes exothermically.
(iii) *Manufacture of NH${}_3$ etc *liquid nitrogen as cooling agent * gas carrier in gas chromatography * as preventive against oxidation.

(c)(i) Dilute H${}_2$SO${}_4$ reacts with CaCO${}_{3(s)}$ to form our insoluble salt CaSO${}_4$, which covers the CaCO${}_3$, thus preventing further reaction or production of CO${}_{2(g)}$ , after a short time. (ii) Conc. H${}_2$SO${}_4$ reacts with ammonia to form a salt (NHq)${}_2$SO${}_4$

(d)i) Physical Properties of Metals * / ductility *Good conductor of heat / electricity *Sonorous *relatively high density * high melting / boiling points
(ii) Chemical Properties of Metals * Ionize by electron loss / reducing agent *Form basic oxides *(some) displace hydrogen from dilute oxide *A more reactive metal displaces or loss reactive metal from a solution cf its salt.
(e)(i) (I) Oxidation no of CI = 0
(II) Oxidation no of CI = + 5
(ii) Oxidation no of V = + 5
(f)(i) Half - life is the time taken for half of the total number of atoms in a given sample of the element to decay.
(ii)(I) Q is more stable
(II) Stability is dependent on half life, the longer it takes substance to decay the more stable it is.