A flask contains a mixture of compounds A and B. Both compounds decompose by first-order kinetics. The half-lives for A and B are 300 s and 180 s, respectively. If the concentrations of A and B are equal initially, the time required for the concentration of A to be four times that of B(in s) :
(Use ln 2 = 0.693)

The most appropriate reagent for conversion of C₂H₅CN into CH₃CH₂CH₂NH₂ is

The structure of PCl₅ in the solid state 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 :