How are atomic orbitals (electrons) identified or distinguished?

The electronic configurations of four elements are given in brackets: $L\,(1s^2, 2s^2 2p^1)$; $M\,(1s^2, 2s^2 2p^5)$; $Q\,(1s^2, 2s^2 2p^6, 3s^1)$; $R\,(1s^2, 2s^2 2p^2)$. Which element would most readily form a diatomic molecule?

Possible number of orientations of a subshell is

Which orbital has two angular nodal planes?

Which of the following ions has $18$ electrons in its outermost shell?

Electronic configuration of $H^{-}$ is