Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them:
$(a)$ Ammonia
$(b)$ Carbon monoxide
$(c)$ Hydrogen chloride
$(d)$ Aluminium fluoride
$(e)$ Magnesium sulphide

(N/A) To find the ratio by mass,we divide the total mass of each element in the formula by the atomic mass of the elements.
$(a)$ Ammonia $(NH_3)$: Atomic masses are $N=14$,$H=1$. Ratio $N:H = 14 : (3 \times 1) = 14:3$.
$(b)$ Carbon monoxide $(CO)$: Atomic masses are $C=12$,$O=16$. Ratio $C:O = 12:16 = 3:4$.
$(c)$ Hydrogen chloride $(HCl)$: Atomic masses are $H=1$,$Cl=35.5$. Ratio $H:Cl = 1:35.5 = 2:71$.
$(d)$ Aluminium fluoride $(AlF_3)$: Atomic masses are $Al=27$,$F=19$. Ratio $Al:F = 27 : (3 \times 19) = 27:57 = 9:19$.
$(e)$ Magnesium sulphide $(MgS)$: Atomic masses are $Mg=24$,$S=32$. Ratio $Mg:S = 24:32 = 3:4$.