Identify isoelectronic pair from following.

When 0.01 mole of nonvolatile solute is dissolved in certain solvent calculate the mass of solvent in kg if $\Delta \mathrm{T}_{\mathrm{b}}=0.6 \mathrm{~K}$ and $\mathrm{K}_{\mathrm{b}}$ for solvent= $2 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$

Which from following polymers contains $-\mathrm{CO}-\mathrm{NH}-$ linkage?

Identify the amine having highest $\mathrm{pK}_{\mathrm{b}}$ value.