Which among the following pairs of compounds is not isomorphous?

Which among the following compounds is used as selective weed killer?

Calculate the difference between heat of combustion of carbon monoxide gas at constant pressure and at constant volume at $27^{\circ} \mathrm{C} ?\left(R=2 \mathrm{cal} \mathrm{K}^{-1} \mathrm{~mol}^{-1}\right)$

The conductivity of an electrolytic solution decreases on dilution due to