Question

Which is true about effective nuclear charge.
(A) $Z_{eff}=Z-\sigma$ (is Screening Constant)
(B) $Z_{eff}$ increases as we move from left to right in Periodic Table
(C) $Z_{eff}$ decreases from top to bottom
(D) $Z_{eff}$ increases from top to bottom

• A. Only (A)
• B. Only (B)
• C. Both (A) and (B)
• D. (A), (B), (C) only

Answer 1

The correct option is D (A), (B), (C) only

As $Z_{eff}=Z_0-\sigma$
where $\sigma$ is screening Constant or shielding constant

Effective nuclear charge increases across the period from left to right because across the period $Z_0$ increases more as compared to shielding constant, so overall $Z_{eff}$ will increase across the period from left to right .

And effective nuclear charge decreases down the group since shielding constant increases more as compared to $Z_0$, so overall $Z_{eff}$ will decrease as we move from top to bottom.