back to directory
NEET CHEMISTRYClassification of Elements and Periodicity in PropertiesMedium

Question

The correct order of first ionization enthalpy for the given four elements is:

A

C < N < F < O

B

C < N < O < F

C

C < O < N < F

D

C < F < N < O

Step-by-Step Solution

Generally, ionization enthalpy increases across a period from left to right due to increasing effective nuclear charge. Thus, we expect the order C < N < O < F. However, there is an anomaly between Nitrogen (Group 15) and Oxygen (Group 16). Nitrogen has a stable exactly half-filled electronic configuration (1s22s22p31s^2 2s^2 2p^3). Oxygen (1s22s22p41s^2 2s^2 2p^4) has two electrons paired in one 2p orbital, resulting in electron-electron repulsion that makes it easier to remove one electron compared to the stable configuration of Nitrogen. Therefore, the first ionization enthalpy of Oxygen is lower than that of Nitrogen. The correct order is C < O < N < F.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Classification of Elements and Periodicity in Properties. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYClassification of Elements and Periodicity in Propertiescorrectionizationenthalpyelements

More Classification of Elements and Periodicity in Properties Questions

View all

The correct sequence of increasing radii is:

A.Ar < K⁺ < Ca²⁺
B.Ca²⁺ < Ar < K⁺
C.Ca²⁺ < K⁺ < Ar
D.K⁺ < Ar < Ca²⁺
EasySolve

Which one of the following represents all isoelectronic species?

A.Na⁺, Cl⁻, O⁻, NO⁺
B.N₂O, N₂O₄, NO⁺, NO
C.Na⁺, Mg²⁺, O⁻, F⁻
D.Ca²⁺, Ar, K⁺, Cl⁻
EasySolve

The value of electron gain enthalpy of $Na^+$, if $IE_1$ of Na = 5.1 eV, is:

A.+10.2 eV
B.–5.1 eV
C.–10.2 eV
D.+2.55 eV
EasySolve

Be²⁺ is isoelectronic with which of the following ions?

A.H⁺
B.Li⁺
C.Na⁺
D.Mg²⁺
EasySolve

Identify the correct order of the size of the following species: $Ca^{2+}, K^+, Ar, S^{2-}, Cl^-$

A.$Ca^{2+} < K^+ < Ar < S^{2-} < Cl^-$
B.$Ca^{2+} < K^+ < Ar < Cl^- < S^{2-}$
C.$Ar < Ca^{2+} < K^+ < Cl^- < S^{2-}$
D.$Ca^{2+} < Ar < K^+ < Cl^- < S^{2-}$
MediumSolve

The formation of the oxide ion O²⁻(g) from oxygen atom requires first an exothermic and then an endothermic step as shown below: O(g) + e⁻ → O⁻(g); ΔH° = -141 kJ mol⁻¹ O⁻(g) + e⁻ → O²⁻(g); ΔH° = +780 kJ mol⁻¹ Thus, the process of formation of O²⁻ in gas phase is unfavourable even though O²⁻ is isoelectronic with neon. It is due to the fact that:

A.Electron repulsion outweighs the stability gained by achieving noble gas configuration
B.O⁻ ion has comparatively smaller size than oxygen atom
C.Oxygen is more electronegative
D.Addition of electron in oxygen result in large size of the ion
MediumSolve

Which of the following arrangements is correct for increasing order of electronegativity?

A.Si < C < O < N < F
B.O < F < N < C < Si
C.F < O < N < C < Si
D.Si < C < N < O < F
EasySolve

The correct order of decreasing second ionization enthalpy of Ti(22), V(23), Cr(24) and Mn(25) is:

A.Cr > Mn > V > Ti
B.V > Mn > Cr > Ti
C.Mn > Cr > Ti > V
D.Ti > V > Cr > Mn
MediumSolve

Why 32,000+ students choose TopperSquare

Everything you need to crack NEET

15,000+ Chapter MCQs

Physics, Chemistry, Biology — chapter-wise, topic-wise practice

AI Performance Analytics

Know your weak topics. Get a personalised study plan.

Full NEET Mock Tests

180 questions, timed, with detailed score analysis

PYQ Sets 2010–2024

15 years of past papers with solved explanations

Start Practising Free

No credit card · 30-second signup · Free forever plan included

This neet chemistry practice question is part of the TopperSquare free question bank. TopperSquare offers 15,000+ chapter-wise NEET MCQs across Physics, Chemistry, and Biology with detailed step-by-step explanations, full mock tests, NEET PYQs (2010–2024), and an AI-powered performance analytics dashboard. browse all neet practice questions → · practice chemistry sets →

Explore more subjects:Physics MCQs•Chemistry MCQs•Biology MCQs•Botany MCQs•Zoology MCQs•NEET Mock Tests•NEET PYQs