Question

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:

• 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
• D. Both A and R are true but R is NOT the correct explanation of A

Answer 1

Answer: (C)

A is false but R is true

Answer 2

- The statement in Assertion A is incorrect because the first ionisation enthalpy actually increases across a period, not decreases. This is due to the increasing effective nuclear charge as we move across a period, which holds the electrons more tightly, making it harder to remove them.

- The statement in Reason R is true; the increase in nuclear charge indeed outweighs the shielding effect across a period, leading to a higher ionisation enthalpy.

Thus, A is false but R is true.

So, the correct answer is: Option (3)