The number of significant figures in 0.00340 is ____________.

Assuming that Ba(OH)₂ is completely ionised in aqueous solution under the given conditions the concentration of H₃O⁺ ions in 0.005 M aqueous solution of Ba(OH)² at 298 K is ______________ $$\times$$ 10^$$-$$12 mol L^$$-$$1. (Nearest integer)

0.8 g of an organic compound was analyzed by Kjeldahl's method for the estimation of nitrogen. If the percentage of nitrogen in the compound was found to be 42%, then ______________ mL of 1 M H₂SO₄ would have been neutralized by the ammonia evolved during the analysis.

When 3.00 g of a substance 'X' is dissolved in 100 g of CCl₄, it raises the boiling point by 0.60 K. The molar mass of the substance 'X' is ______________ g mol^$$-$$1. (Nearest integer).

[Given K_b for CCl₄ is 5.0 K kg mol^$$-$$1]