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JEE Main levelSingle correct optionDifficulty 2 of 3pt194

Why does electronegativity (Allred-Rochow type reasoning, $χ \propto Z_{e ff} / r^{2}$ ) generally decrease down a group?

AThe effective nuclear charge falls sharply
BThe atomic radius increases much faster than $Z_{e ff}$ changes, so the force on a bonding pair decreases
CThe number of valence electrons decreases
DThe nuclear charge decreases

Answer: B

The electrostatic pull on a bonding pair scales as

Z_{e ff} / r^{2}

. Down a group

Z_{e ff}

for the valence shell changes little, but the radius increases markedly, so the pull falls and electronegativity decreases.

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