Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them. (You may use appendix-III). 
(a) Ammonia
(b) Carbon monoxide
(c) Hydrogen chloride
(d) Aluminium fluoride
(e) Magnesium sulphide
Ans. (a) NH3; ratio N : H = 14 : 3
 (b) CO; ratio C : O = 3 : 4
 (c) HCl; ratio H : Cl = 1 : 35.5 or 2 : 71
 (d) AlF₃; ratio Al : F = 9 : 19
 (e) MgS; ratio Mg : S = 3 : 4 

(a) CO₂³⁻
Ans. 4
(b) PO₄³⁻
Ans. 5
(c) P₂O₅
 Ans. 7
 (d) CO
 Ans. 2

Yes, it is a temperature dependent property. The solubility generally, increases with increase in temperature. For example, you can dissolve more sugar in hot water than in cold water.

(a) F₂
(b) NO₂
(c) N₂O
(d) C₂H₆
(e) P₄
(f) H₂O₂
(g) P₄O₁₀
(H) O₃
(i) HCl
(j) CH₄
(k) He
(l) Ag
Ans. (a) 2 atom
(b) 3 atom
(c) 3 atom
(d) 8 atom
(e) 4 atom
(f) 4 atom
(g) 14 atom
(h) 3 atom
(i) 2 atom
(j) 5 atom
(k) 1 atom (noble gases are always monoatomic)
(l) Polyatomic (because metals are bound by metallic bond and any measurable quantity
of a metal can contain millions of atoms.)

On heating the powder, it will char if it is a sugar. Alternatively, the powder may be dissolved in water and checked for its conduction of electricity. If it conducts, it is a salt.

Number of moles = mass/molar mass = 12 g/24 g = 0.5 mol

(a) 5 moles of CO₂ and 5 moles of H₂O do not have the same mass.
Ans. CO₂ has molar mass = 44g mol^–1
5 moles of CO₂ have molar mass = 44 × 5 = 220 g
H₂O has molar mass = 18 g mol^–1
5 moles of H₂O have mass = 18 × 5 g = 90 g