$\mu$-meson of charge $e$, mass $208 m_e$ moves in a circular orbit around a heavy nucleus having charge $+3 e$. The quantum state $n$ for which the radius of the orbit is same as that of the first Bohr orbit for hydrogen atom is (approximately]

A nucleus with atomic mass number $A$ produces another nucleus by loosing 2 alpha particles. The volume of the new nucleus is 60 times that of the alpha particle. The atomic mass number $A$ of the original nucleus is

A hydrogen atom falls from $n$th higher energy orbit to first energy orbit $(n=1)$. The energy released is equal to 12.75 eV . The $n$th orbit is

The decrease in each day in the uranium mass of the material in a uranium reactor operating at a power of 12 MW is (Energy released in one ${ }_{92} \mathrm{U}^{235}$ fission is about 200 MeV )