Geometrical shapes of the complexes formed by the reaction of Ni²⁺ with Cl^-, CN^- and H₂O respectively are

According to kinetic theory of gases

To an evacuated vessel with movable piston under external pressure of 1 atm, 0.1 mol of He and 1.0 mol of an unknown compound (vapour pressure 0.68 atm, at 0^oC) are introduced. Considering the ideal gas behaviour, the total volume (in litre) of the gases at 0^oC is close to

Among the following compounds, the most acidic is