The element whose percentage composition in an organic compound can be determined by Carius method is

' $x$ ' mg of an organic compound was analysed by Kjeldahl method. The ammonia evolved was absorbed in 50 mL of $0.5 \mathrm{M} \mathrm{H}_2 \mathrm{SO}_4$. The unused acid required 60 mL of 0.5 M NaOH solution for complete neutralisation. If the percentage of nitrogen in the compound is 56 , the value of $x$ is

The composition of a sample of wustite is $\mathrm{Fe}_{0.93} \mathrm{O}_{1.00}$. Percentage of iron in the form of $\mathrm{Fe}^{3+}$ ion is nearly

A solution of urea in water has a boiling point or $100.18^{\circ} \mathrm{C}$. What is the freezing point of the same solution, if $K_f$ and $K_b$ of water are 1.86 and 0.52 K kg $\mathrm{mol}^{-1}$.