UPSC Prelims 2001 · General Studies
Question 121: Science and Technology
Consider the following statements with reference to the Periodic Table of chemical elements: I. Ionisation potential gradually decreases along a period. II. In a group of elements, electron affinity decreases as the atomic weight increases. III. In a given period, electronegativity decreases as the atomic number increases. Which of these statement(s) is/are correct?
AnswerThe answer is (b).
Only statement II is correct. In general, electron affinity decreases down a group because atoms get bigger and the added electron is further from the nucleus. Statement I is wrong because ionisation potential generally rises along a period, as nuclear charge increases while atoms shrink; statement III is wrong because electronegativity also increases along a period. Remember that along a period ionisation energy and electronegativity both increase.
- I. Ionisation potential generally increases along a period.
- II. Electron affinity generally decreases down a group.
- III. Electronegativity increases along a period.
Why each option is right or wrong
- (a) I is wrong; ionisation potential rises along a period.
- (b) Right: only II.
- (c) I and III are both wrong.
- (d) III is wrong, as electronegativity increases along a period.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.