In Bohr's theory of hydrogen atom, 'r' is the radius of the orbit, 'V' is the speed of electron and E is the total energy of the electron. Out of the following which physical quantity is inversely proportional to principal quantum number?

In common emitter mode of transistor, the d.c. current gain is $20$, the emitter current is $7$ mA. The collector current is

In the case of NAND gate, if A and B are inputs and Y is the output then

In energy band diagram of insulators, a band gap and the conduction band is respectively