The number of nodal planes (planes of zero electron density) in the $d_{xy}$ orbital is:

Which of the following sets of quantum numbers belongs to the highest energy?

Which of the following is not a permissible arrangement of electrons in an atom?

For the given quantum numbers $n$ and $l$ of electrons:
$(i) n = 4, l = 1$
$(ii) n = 4, l = 0$
$(iii) n = 3, l = 2$
$(iv) n = 3, l = 1$
Arrange them in the increasing order of their energy.

An element has the electronic configuration $1s^2, 2s^2 2p^6, 3s^2 3p^2$. Its valence electrons are

There is no difference between a $2p$ and a $3p$ orbital regarding