If uncertainty in position and momentum of an electron are equal, then uncertainty in its velocity is

The graph between variation of probability density. $\psi^2(r)$ and distance of the electron from the nucleus, $r$ is shown below. This represents

The angular momentum of an electron in a stationary state of $\mathrm{Li}^{2+}(Z=3)$ is $3 h / \pi$. The radius and energy of that stationary state are respectively

Identify the pair of elements in which number of electrons in ( $n-1$ ) shell is same