JEE Main 2020 · 2 September · morning · Single correct · +4 / −1
In general the property (magnitudes only) that show an opposite trend in comparison to other properties across a period is
- (a) Electron gain enthalpy
- (b) Electronegativity
- (c) Ionization enthalpy
- (d) Atomic radius
Answer and solution
Answer (d) Atomic radius
Solution
Chemistry ma’am · 3 steps
Across a period the nucleus pulls harder, so everything grows except the size of the atom.
- What changes. Moving left to right, the nuclear charge rises by one each step, but the new electron goes into the same shell. Shielding barely improves, so the effective nuclear charge on the outer electrons keeps increasing.
- Its effect. A stronger pull draws the outer shell inward, so the atom shrinks. The same strong pull makes the atom hold its own electrons and grab new ones more tightly.
Property Trend in magnitude across a period Electron gain enthalpy increases (becomes more negative) Electronegativity increases Ionization enthalpy increases Atomic radius decreases - So. Atomic radius is the only one that goes down while the other three go up, so the answer is (d).
The idea to keep. Across a period the effective nuclear charge rises. Anything about holding or attracting electrons goes up, and atomic size goes down. Size always runs opposite to these three.
Answer from the NTA final answer key. Solution by PrepWiser.