Chemistry · Periodicity of Elements and Periodic Properties
JEE Main 2024 — 29 January, Shift 1 — Question 59
Given below are the two statements, one is labelled 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 answer from the options given below:
- Option A:
Both (A) and (R) are true and (R) is the correct explanation of (A)
- Option B:
Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
- Option C:
(A) is true, but (R) is false
- Option D:Correct
(A) is false, but (R) is true
Answer: D
Step-by-step solution
Assertion (A): Across a period, effective nuclear charge increases. Therefore electrons are held more strongly. Hence first ionisation enthalpy generally increases across a period, not decreases. So, Assertion is false.
Reason (R): Across a period, nuclear charge increases while shielding remains nearly constant. Thus effective nuclear charge increases. So, Reason is true.
Therefore, the correct option is D.
Answer key and solution verified before publishing.
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- Exam
- JEE Main 2024
- Paper
- 29 January, Shift 1
- Subject
- Chemistry
- Chapter
- Periodicity of Elements and Periodic Properties
- Topic
- Periodicity in Chemical Properties (Ionization Energy, Electron Affinity, Electronegativity)