GS PrelimsScience and TechnologyGeneral Science2001

Consider the following statements with reference to the Periodic Table of chemical elements: 1. Ionisation potential gradually decreases along a period. 2. In a group of elements, electron affinity decreases as the atomic weight increases. 3. In a given period, electronegativity decreases as the atomic number increases. Which of these statement(s) is/are correct?

A

I only

B

II only

C

I and III

D

II and III

Correct Answer: Option B

Explanation

1. Statement 1: Ionisation potential (or ionization energy) generally *increases* along a period in the Periodic Table from left to right, because the effective nuclear charge increases, holding electrons more tightly. (Incorrect) 2. Statement 2: In a group of elements, as atomic weight (and atomic size) increases down the group, the outermost electron is further from the nucleus and shielded by inner electrons. This generally leads to a *decrease* in electron affinity (energy released when an electron is added). (Correct) 3. Statement 3: Electronegativity, the tendency of an atom to attract bonding electrons, generally *increases* along a period as the atomic number increases, due to increasing effective nuclear charge. (Incorrect) 4. Therefore, only statement 2 is correct.

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