Which of following bonds has maximum bond length?

Which of the following sets of components form homogeneous mixture?

Which among the following compounds in crystalline form is used for making Nicol's prism?

Two electrolytic cells are connected in series containing $\mathrm{CuSO}_4$ solution and molten $\mathrm{AlCl}_3$. If in electrolysis 0.4 moles of 'Cu' are deposited on cathode of first cell. The number of moles of 'Al' deposited on cathode of the second cell is