Chapter Exam

Unit 9: Classification of Elements and Periodicity in Properties — Online MCQ Test

Q: Which among the following electronic configurations belong to main group elements? A. [Ne]3s¹ B. [Ar]3d³4s² C. [Kr]4d¹⁰5s²5p⁵ D. [Ar]3d¹⁰4s¹ E. [Rn]5f⁰6d²7s²

Answer: B. A and C only — Main group elements have s or p orbitals as the valence shell (s-block and p-block). A ([Ne]3s¹) and C ([Kr]4d¹⁰5s²5p⁵) are main group elements. B, D, and E are transition or inner-transition metals.

Q: In which of the following options the order of arrangement does not agree with the variation of property indicated against it?

Answer: A. B < C < N < O (increasing first ionisation enthalpy) — First IE of Nitrogen is higher than Oxygen due to stable half-filled 2p subshell (2p3). Electron gain enthalpy of Fluorine is less negative than Chlorine due to small size and inter-electronic repulsion. Both A and B are technically incorrect statements.

Q: Which one of the following orders in correct for the bond dissociation enthalpy of halogen molecules?

Answer: A. Cl2 > Br2 > F2 > I2 — Due to the small size of the fluorine atom, the lone pairs have significant inter-electronic repulsion, weakening the F-F bond. Thus, Cl2 has the highest bond dissociation enthalpy.

Q: Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules ?

Answer: A. Cl2 > Br2 > F2 > I2 — The bond dissociation enthalpy of F2 is lower than that of Cl2 and Br2 due to the small size of the fluorine atom, which leads to strong inter-electronic repulsion between the lone pairs.

Q: Magnesium reacts with an element (X) to form an ionic compound. If the ground state electronic configuration of (X) is 1s² 2s² 2p³, the simplest formula for this compound is

Answer: B. Mg₃X₂ — Element X with configuration 1s² 2s² 2p³ is nitrogen (N), which has 5 valence electrons and forms X³⁻ ion (gaining 3 electrons to complete octet). Magnesium forms Mg²⁺ ion. To balance charges: 3 Mg²⁺ provides +6 charge; 2 N³⁻ provides −6 charge. So the formula is Mg₃X₂ (analogous to Mg₃N₂).

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Practice Unit 9: Classification of Elements and Periodicity in Properties with a free chapter-wise online MCQ test for NEET NEET (All) CHEMISTRY. This chapter covers: Modem periodic law and present form of the periodic table s p. d and f block elements periodic trends in properties of elements atomic and ionic radii ionization enthalpy electron.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Unit 9: Classification of Elements and Periodicity in Properties — Important Questions & Answers (FAQ)

Frequently asked questions from NEET NEET (All) CHEMISTRY — Unit 9: Classification of Elements and Periodicity in Properties, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which among the following electronic configurations belong to main group elements? A. [Ne]3s¹ B. [Ar]3d³4s² C. [Kr]4d¹⁰5s²5p⁵ D. [Ar]3d¹⁰4s¹ E. [Rn]5f⁰6d²7s²

A. B and E only
B. A and C only ✓
C. D and E only
D. A, C and D only

Answer: B. A and C only
Main group elements have s or p orbitals as the valence shell (s-block and p-block). A ([Ne]3s¹) and C ([Kr]4d¹⁰5s²5p⁵) are main group elements. B, D, and E are transition or inner-transition metals.

In which of the following options the order of arrangement does not agree with the variation of property indicated against it?

A. B < C < N < O (increasing first ionisation enthalpy) ✓
B. I < Br < Cl < F (increasing electron gain enthalpy)
C. Li < Na < K < Rb (increasing metallic radius)
D. Al3+ < Mg2+ < Na+ < F- (increasing ionic size)

Answer: A. B < C < N < O (increasing first ionisation enthalpy)
First IE of Nitrogen is higher than Oxygen due to stable half-filled 2p subshell (2p3). Electron gain enthalpy of Fluorine is less negative than Chlorine due to small size and inter-electronic repulsion. Both A and B are technically incorrect statements.

Which one of the following orders in correct for the bond dissociation enthalpy of halogen molecules?

A. Cl2 > Br2 > F2 > I2 ✓
B. Br2 > I2 > F2 > Cl2
C. F2 > Cl2 > Br2 > I2
D. I2 > Br2 > Cl2 > F2

Answer: A. Cl2 > Br2 > F2 > I2
Due to the small size of the fluorine atom, the lone pairs have significant inter-electronic repulsion, weakening the F-F bond. Thus, Cl2 has the highest bond dissociation enthalpy.

Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules ?

A. Cl2 > Br2 > F2 > I2 ✓
B. Br2 > I2 > F2 > Cl2
C. F2 > Cl2 > Br2 > I2
D. I2 > Br2 > Cl2 > F2

Answer: A. Cl2 > Br2 > F2 > I2
The bond dissociation enthalpy of F2 is lower than that of Cl2 and Br2 due to the small size of the fluorine atom, which leads to strong inter-electronic repulsion between the lone pairs.

Magnesium reacts with an element (X) to form an ionic compound. If the ground state electronic configuration of (X) is 1s² 2s² 2p³, the simplest formula for this compound is

A. Mg₂X₃
B. Mg₃X₂ ✓
C. Mg₂X
D. MgX₂

Answer: B. Mg₃X₂
Element X with configuration 1s² 2s² 2p³ is nitrogen (N), which has 5 valence electrons and forms X³⁻ ion (gaining 3 electrons to complete octet). Magnesium forms Mg²⁺ ion. To balance charges: 3 Mg²⁺ provides +6 charge; 2 N³⁻ provides −6 charge. So the formula is Mg₃X₂ (analogous to Mg₃N₂).