A) lanthanide contraction
B) the fact that successive addition of d-electrons screen the outer electrons (4s) from the inward pull of the nucleus
C) increase in radii due to increase in 'n' is compensated by decrease in radii due to increase in effective nuclear charge (Z)
D) atomic radii do not remain constant but decrease in a normal gradation
Correct Answer: B
Solution :
[b] After mid-way i.e., after Cr as the elctrons enters the last but one shell, the added d-electron shields the outer most electrons. Hence with the increase in the d-electrons screening effect increases. This counter blances the increased nuclear charage. As a result, the atomic radii remain paractically same after chromium.
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