Calculate the percentage by weight of :

(a) C in carbon dioxide

(b) Na in sodium carbonate

(c) Al in aluminium nitride.

[C = 12, O = 16, H = 1, Na = 23, Al = 27, N = 14]

Calculate which of the following — calcium nitrate or ammonium sulphate has a higher % of nitrogen. [Ca = 40, , O = 16, S = 32, N = 14]

Calculate the percentage of pure aluminium in 10 kg. of aluminium oxide [Al₂O₃] of 90% purity. [Al = 27, O = 16]

State which of the following are better fertilizers —

(i) Potassium phosphate [K₃PO₄] or potassium nitrate [KNO₃]

(ii) Urea [NH₂CONH₂] or ammonium phosphate [(NH₄)₃PO₄]

[K = 39, P = 31, O = 16, N = 14, H = 1]