The radius of the second Bohr orbit, in terms of the Bohr radius, a₀, in Li²⁺ is :

For the following Assertion and Reason, the correct option is :

Assertion : The pH of water increases with increase in temperature.

Reason : The dissociation of water into H⁺ and OH^– is an exothermic reaction.

Arrange the following bonds according to their average bond energies in descending order :
C–Cl, C–Br, C–F, C–I

A metal (A) on heating in nitrogen gas gives compound B. B on treatment with H₂O gives a colourless gas which when passed through CuSO₄ solution gives a dark blue-violet coloured solution. A and B respectively, are :