QJEEM25Ch2b19: JEE Main 2025 Chemistry - Class 11 JEEM25Ch2b19 Solution: The incorrect decreasing order of atomic radii is

The incorrect order is Be > Mg > Al > Si.

• Atomic radius increases down a group because the number of electron shells increases. Since $\mathrm{Mg}$ is below $\mathrm{Be}$ in Group 2, $\mathrm{Mg}$ must be larger than $\mathrm{Be}$ ( \mathrm{Mg} > \mathrm{Be} ).
• Atomic radius decreases across a period (left to right) due to increasing effective nuclear charge. In Period 3, the order is \mathrm{Mg} > \mathrm{Al} > \mathrm{Si} .

Combining these trends, the correct decreasing order is: \mathrm{Mg} > \mathrm{Al} > \mathrm{Si} > \mathrm{Be}