What is the effective nuclear charge experienced by the 2p and 3p electrons of a chlorine atom, respectively?

Effective nuclear charge Zeff can be calculated as:

Zeff = Z - s

where Z is the nuclear charge (=17 for Cl) while s is the screening by all the other e⁻s.

The electronic configuration is:

[1s^2][2s^2 2p^6][3s^2 3p^5]

The s for [2s^2 2p^6] part = 8 * 0.85 = 6.8

The s for [3s^2 3p^4] part = 6 * 0.35 = 2.1

So,

Zeff (2p) = 17 - 6.8 = 10.2

Zeff (3p) = 17 - 2.1 = 14.9