Given below are two statements :

Statement I : There are several conformers for n -butane. Out of those conformers,

Statement II : As the dihedral angle increases, torsional strain decreases from (X) to $(\mathrm{Y})$.

In the light of the above statements, choose the correct answer from the options given below

In the Group analysis of cations, $\mathrm{Ba}^{2+} $ & $\mathrm{Ca}^{2+}$ are precipitated respectively as

" X " is an oxoanion of the lightest element of group 7 (in the periodic table). The metal is in +6 oxidation state in " X ". The color of the potassium salt of X is

At 298 K , the mole percentage of $\mathrm{N}_2(\mathrm{~g})$ in air is $80 \%$. Water is in equilibrium with air at a pressure of 10 atm . What is the mole fraction of $\mathrm{N}_2(\mathrm{~g})$ in water at 298 K ? $\left(\mathrm{K}_{\mathrm{H}}\right.$ for $\mathrm{N}_2$ is $\left.6.5 \times 10^7 \mathrm{~mm} \mathrm{Hg}\right)$