The increasing order of energy of the orbitals 3s,3p,3d,4s  is

The increasing order of energy of the orbitals is depend on both n and l values. If the n l + value is greater for one orbital it has high energy than other orbitals with their n l + value is minimum. Here, the given 3s ,3p ,3d and 4s  orbitals having n +l  values are 3 +0 =3, 3 +1= 4, 3+ 2=5 and 4+0=4respectively. Therefore, the increasing order of energy of the orbitals 3s,3p,3d,4s is 3s<3p<4s<3d