The figure shows standing de-Broglie waves due to the revolution of electron in a certain orbit of hydrogen atom. Then, the expression for the orbit radius is (All notations have their usual meanings)

An electron in an excited state of $$\mathrm{Li}^{2+}$$ ion has angular momentum $$\frac{3 h}{2 \pi}$$. The de-Broglie wavelength of electron in this state is $$p \pi a_0$$ (where, $$a_0=$$ Bohr radius). The value of $$p$$ is

Which graph in the following diagram correctly represents the potential energy of a pair of nucleons as a function of their separation?

In a nuclear reactor heavy nuclei is not used as moderators because