An aqueous solution of sodium sulphate is acidic in nature.

The solubility product of silver chloride in water decreases on the addition of potassium chloride to the solution.

Which of the following solutions will have a lower vapour pressure and why ?

(1) A 5% solution of cane sugar (C_I2H₂₂O₁₁)

(2) A 5% solution of urea (NH₂CO NH₂)

(Relative atomic masses: H = 1, C = 12, 0 = 16, N = 14).

(i) In a body centred and face centred arrangement of atoms of an element, what will be the number of atoms present in respective unit cells?   

(ii) Explain why graphite is soft and can be used an a lubricant.

19. 1.0 gm. of strontium - 90 was reduced to 0.953 gm after two years. Calculate the half- life period of strontium - 90.