Assertion A: The first ionisation enthalpy decreases across a period.

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: 

(1) Both A and R are true and R is the correct explanation of A 

(2) A is true but R is false 

(3) A is false but R is true 

(4) Both A and R are true but R is NOT the correct explanation of A

Answer 1

(3) A is false but R is true 

First ionisation energy increases along the period. Along the period Z increases which outweighs the shielding effect.