Identify the element having the electronic configuration $1s^2, 2s^2, 2p^2$.

Assertion :- In $H$-atom,the energy of $3d$-level is smaller than $4s$-level.
Reason :- In multi-electron species,an orbital with lower value of $(n+\ell)$ has energy smaller than the orbital with larger value of $(n+\ell)$.

Which of the following sets of quantum numbers is correct for an electron in $4f$ orbital?

Write about $p$-orbitals.

The four quantum numbers for the unpaired electron of chlorine $(Cl)$ are:

Compare the energies of the following sets of quantum numbers for a multielectron system:
$A. n=4, \ell=1$
$B. n=4, \ell=2$
$C. n=3, \ell=1$
$D. n=3, \ell=2$
$E. n=4, \ell=0$
Choose the correct answer from the options given below: