Arrange the $1s$,$2s$,$4s$,$2p$,$3p$,$4p$,and $3d$ orbitals according to increasing order of energy.

(N/A) The energy of orbitals is determined by the $(n+l)$ rule.
According to this rule,the orbital with a lower $(n+l)$ value has lower energy.
If the $(n+l)$ values are the same,the orbital with the lower principal quantum number $(n)$ has lower energy.
Based on this,the increasing order of energy is: $1s < 2s < 2p < 3p < 4s < 3d < 4p$.

Orbital Properties	Explanation
$1s$: $n=1, l=0, n+l=1$	Lowest energy
$2s$: $n=2, l=0, n+l=2$	-
$2p$: $n=2, l=1, n+l=3$	-
$3p$: $n=3, l=1, n+l=4$	-
$4s$: $n=4, l=0, n+l=4$	$3p$ $(n=3)$ < $4s$ $(n=4)$
$3d$: $n=3, l=2, n+l=5$	-
$4p$: $n=4, l=1, n+l=5$	$3d$ $(n=3)$ < $4p$ $(n=4)$