Among the following pairs of orbitals which orbital will experience the large effective nuclear charge? (i) 2s and 3s  (ii) 4d and 4f  (iii) 3d and 3p.

Force of attraction between nucleus and the electron present around it depend upon the distance between the nucleus and the orbital, in which electron present. As the distance increases, the effective nuclear charge also decreases. 

(i) Out of 2s and 3s orbitals: 2s orbital is closer to the nucleus than 3s orbital. Hence 2s orbital will experience larger effective nuclear charge.
(ii) Out of 4d and 4f orbitals:  4d orbital is closer to the nucleus than 4f orbital. Hence 4d orbital will experience larger effective nuclear charge.
(iii) Out of 3d and 3p orbitals: 3p orbital is closer to the nucleus than 3d orbital. Hence 3p orbital will experience large effective nuclear charge.