When the speed of light becomes $$\frac{2}{3}$$ of its present value, then the energy released in a given atomic explosion would

An electron of an atom transits from $$n_1$$ to $$n_2$$. In which of the following maximum frequency of photon will be emitted?

Two protons are kept at a separation of 40 $$\mathop A\limits^o $$. F$$_n$$ is the nuclear force and F$$_e$$ is the electrostatic force between them. Then,

Two radioactive materials X$$_1$$ and X$$_2$$ have decay constant 5$$\lambda$$ and $$\lambda$$, respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X$$_1$$ to X$$_2$$ will be $$1/e$$ after a time