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]

(i) Molecular weight of K₃PO₄ = 3(39) + 31 + 4(16) = 117 + 31 + 64 = 212 g

Percentage of K in K₃PO₄ = $\dfrac{117}{212}$ x 100 = 55.18%

Molecular weight of [KNO₃] = 39 + 14 + 3(16) = 39 + 14 + 48 = 101 g

Percentage of K in KNO₃ = $\dfrac{39}{101}$ x 100 = 38.61%

Hence, potassium phosphate (% of K = 55.18 %) is better fertilizer than potassium nitrate (% of K = 38.61 %).

(ii) Molecular weight of NH₂CONH₂ = 14 + 2(1) + 12 + 16 + 14 + 2(1) = 14 + 2 + 12 + 16 + 14 + 2 = 60 g

Percentage of N in NH₂CONH₂ = $\dfrac{28}{60}$ x 100 = 46.67%

Molecular weight of (NH₄)₃PO₄ = 3[14 + 4(1)] + 31 + 4(16) = 54 + 31 + 64 = 149 g

Percentage of N in (NH₄)₃PO₄ = $\dfrac{42}{149}$ x 100 = 28.19%

Hence, Urea is a better fertilizer as percentage of N in urea is 46.67% and in (NH₄)₃PO₄ is 28.19 %