JEE Main · 2025 · 28 Jan 2025 · Shift 1 · Classification of Elements and Periodicity

The incorrect decreasing order of atomic radii is :

(A) $Mg > Al > C > O$
(B) $Al > B > N > F$
(C) $Be > Mg > Al > Si$ ✓ Correct
(D) $Si > P > Cl > F$

Answer: (C)

Solution

Atomic radius shrinks across a period as nuclear charge increases and grows down a group as shells are added. Orders (A) Mg>Al>C>O, (B) Al>B>N>F and (D) Si>P>Cl>F all correctly place a larger lower-period atom ahead of smaller, more electronegative upper-period atoms. In (C), Be sits in period 2 while Mg lies directly below it in period 3, so Mg is actually the larger atom of the two — the true order is Be < Mg > Al > Si, not Be > Mg > Al > Si. Option (C) is the incorrect decreasing order.

JEE Main · 2025 · 28 Jan 2025 · Shift 1 · Single correct option

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