Ga (atomic mass 70 u) crystallizes in a hexagonal close packed structure. The total number of voids in 0.581 g of Ga is __________ $$\times$$ 10²¹. (Round off to the Nearest Integer). [Given : N_A = 6.023 $$\times$$ 10₂₃]

When 35 mL of 0.15 M lead nitrate solution is mixed with 20 mL of 0.12 M chromic sulphate solution, _________ $$\times$$ 10^$$-$$5 moles of lead sulphate precipitate out. (Round off to the Nearest Integer).

Sulphurous acid (H₂SO₃) has Ka₁ = 1.7 $$\times$$ 10^$$-$$2 and Ka₂ = 6.4 $$\times$$ 10^$$-$$8. The pH of 0.588 M H₂SO₃ is __________. (Round off to the Nearest Integer).

At 363 K, the vapour pressure of A is 21 kPa and that of B is 18 kPa. One mole of A and 2 moles of B are mixed. Assuming that this solution is ideal, the vapour pressure of the mixture is ___________ kPa. (Round off to the Nearest Integer).