Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: The first ionisation enthalpy decreases across a period.
Reason R: The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements, choose the most appropriate from the options given below:
Assertion A: The first ionisation enthalpy decreases across a period.
Reason R: The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements, choose the most appropriate from the options given below:
- (A)Both A and R are true and R is the correct explanation of A
- (B)A is true but R is false
- (C)A is false but R is true✓ Correct
- (D)Both A and R are true but R is NOT the correct explanation of A
Answer: (C)
Solution
The first ionisation enthalpy generally increases (not decreases) across a period, because the increasing nuclear charge outweighs the extra shielding from added electrons in the same shell.
So Assertion A (decreases across a period) is false, while Reason R (increasing nuclear charge outweighs shielding) is a true statement.
Key confirmed: C (A is false but R is true).
So Assertion A (decreases across a period) is false, while Reason R (increasing nuclear charge outweighs shielding) is a true statement.
Key confirmed: C (A is false but R is true).
JEE Main · 2024 · 29 Jan 2024 · Shift 1 · Single correct option