The increasing order of basicity of the following compounds is :

The difference between the radii of 3^rd and 4^th
orbits of Li²⁺ is R₁ . The difference between the
radii of 3^rd and 4^th orbits of He⁺ is $$\Delta $$R₂ .
Ratio $$\Delta $$R₁ : $$\Delta $$R₂ is :

The structure of PCl₅ in the solid state is :

The most appropriate reagent for conversion of C₂H₅CN into CH₃CH₂CH₂NH₂ is