The order of screening effect of electrons of s, p, d and f orbitals of a given shell of an atom on electrons in its outer shell is :

1. s > p > d > f

2. f > d > p > s

3. p < d < f < s

4. f > p > s > d

HINT: Screening effect depends on the size of orbital.

Explanation:

The screening effect or shielding effect is the phenomenon of reduction of nuclear force of attraction due to inner shell electrons towards valence electrons. The inner shell electrons protect the valence shell electrons from the nuclear force i.e. they shield them.

The order of screening effect of electrons of s, p, d and f orbitals of a given shell of an atom on its outer shell electrons is 

s > p > d > f.

The screening effect decreases from s-orbital to f-orbital in an atom on account of shape of the orbital.