Identify a ligand having two donor atoms but uses a pair of electrons of either donor atom to form coordinate bond.

Which of the following solutions on complete dissociation exhibits maximum elevation in boiling point?

Calculate the entropy change for melting 1 g ice at $0^{\circ} \mathrm{C}$ in $\mathrm{Jg}^{-1} \mathrm{~K}^{-1}$ if heat of fusion of ice at $0^{\circ} \mathrm{C}$ is $80 \mathrm{~J} \mathrm{~K}^{-1}$.

Which pair of elements from following has halt filled d-orbital in observed electronic configuration?