JEE Main levelSingle correct optionDifficulty 2 of 3pt127
Using Slater's rules (same-shell electron 0.35, electrons of the n−1 shell 0.85, deeper electrons 1.00), the effective nuclear charge felt by a 3s electron of Mg (Z=12) is
A3.20
B1.65
C2.85
D3.15
Answer: C
Shielding constant = 1 other 3s electron (0.35) + 8 electrons of n=2 (8 x 0.85 = 6.80) + 2 electrons of n=1 (2 x 1.00 = 2.00) = 9.15. Zeff = 12 - 9.15 = 2.85.