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Solution


Q.

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R:

Assertion A: The first ionization 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:                [2024]
1 A is false but R is true  
2 A is true but R is false  
3 Both A and R are true and R is the correct explanation of A  
4 Both A and R are true but R is NOT the correct explanation of A  

Ans.

(1)

From left to right across a period, number of protons as well as number of electrons increase. Increase in number of protons results in stronger attraction of outermost electron which contributes towards increase of ionization energy. Increase in number of electrons increases inter-electronic repulsion, which contributes towards decrease of ionization energy. Effect of increase in number of protons outweighs the effect of increase in number of electrons. Thus ionization energy increases from left to right across a period. (If nothing is mentioned then trend is taken as left to right across a period).