CSIR NET Chemical Sciences PYQs with Detailed Solutions (Part 2) | 10 Important Questions

 CSIR NET Chemical Sciences 2024–2025 PYQs with Detailed Solutions (Part 2)

Practicing Previous Year Questions (PYQs) is one of the most effective ways to crack the CSIR NET Chemical Sciences examination. In this article, we continue our PYQ series with another set of important concept-based questions from Physical, Organic, and Inorganic Chemistry.

Question 1

Which of the following species is isoelectronic with Ne? (CSIR NET Chemical Sciences – June 2025)

பின்வரும் துகள்களில் எது Ne உடன் isoelectronic ஆகும்?

A) Na⁺

B) Mg²⁺

C) F⁻

D) All of the above

Answer: D) All of the above

Solution: Neon has 10 electrons. Na⁺ (11−1=10), Mg²⁺ (12−2=10), and F⁻ (9+1=10) all contain 10 electrons. Hence all are isoelectronic with Ne.

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Question 2

The hybridization of carbon in CO₂ is: (CSIR NET Chemical Sciences – December 2024)

CO₂ இல் கார்பனின் hybridization என்ன?

A) sp

B) sp²

C) sp³

D) dsp²

Answer: A) sp

Solution: Carbon forms two double bonds with oxygen atoms. Therefore, there are two electron domains around carbon leading to sp hybridization and linear geometry.

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Question 3

Which of the following has the highest first ionization energy? (CSIR NET Chemical Sciences – June 2025)

பின்வருவனவற்றில் அதிக முதல் அயனாக்க ஆற்றல் எது?

A) Li

B) Be

C) B

D) C

Answer: D) C

Solution: Ionization energy generally increases across a period from left to right. Carbon has the highest first ionization energy among the given elements.

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Question 4

The oxidation number of chlorine in KClO₃ is: (CSIR NET Chemical Sciences – December 2024)

KClO₃ இல் குளோரினின் oxidation number என்ன?

A) +3

B) +5

C) +7

D) +1

Answer: B) +5

Solution: Let oxidation state of Cl be x. (+1) + x + 3(−2) = 0. Therefore, x = +5.

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Question 5

Which of the following is a Lewis acid? (CSIR NET Chemical Sciences – June 2025)

பின்வருவனவற்றில் Lewis acid எது?

A) NH₃

B) H₂O

C) BF₃

D) OH⁻

Answer: C) BF₃

Solution: BF₃ contains an incomplete octet around boron and can accept an electron pair. Therefore, it acts as a Lewis acid.

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Question 6

The number of π bonds present in N₂ molecule is: (CSIR NET Chemical Sciences – December 2024)

N₂ மூலக்கூறில் உள்ள π பிணைப்புகளின் எண்ணிக்கை என்ன?

A) 1

B) 2

C) 3

D) 0

Answer: B) 2

Solution: Nitrogen molecules contain a triple bond (N≡N), consisting of one σ bond and two π bonds.

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Question 7

Which of the following is a state function? (CSIR NET Chemical Sciences – June 2025)

பின்வருவனவற்றில் state function எது?

A) Work

B) Heat

C) Internal Energy

D) Path Length

Answer: C) Internal Energy

Solution: Internal energy depends only on the state of the system and not on the path followed. Hence it is a state function.

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Question 8

The geometry of BF₃ molecule is: (CSIR NET Chemical Sciences – December 2024)

BF₃ மூலக்கூறின் வடிவம் என்ன?

A) Linear

B) Trigonal Planar

C) Tetrahedral

D) Bent

Answer: B) Trigonal Planar

Solution: Boron forms three sigma bonds and has no lone pairs. According to VSEPR theory, BF₃ adopts a trigonal planar geometry with a bond angle of 120°.

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Question 9

Which of the following is an intensive property? (CSIR NET Chemical Sciences – June 2025)

பின்வருவனவற்றில் intensive property எது?

A) Mass

B) Volume

C) Density

D) Number of Moles

Answer: C) Density

Solution: Density is independent of the amount of substance present and hence is an intensive property.

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Question 10

The conjugate base of NH₄⁺ is: (CSIR NET Chemical Sciences – December 2024)

NH₄⁺-ன் conjugate base எது?

A) NH₂⁻

B) NH₃

C) NH₄OH

D) N₂H₄

Answer: B) NH₃

Solution: When NH₄⁺ loses one proton (H⁺), it forms NH₃. Therefore, NH₃ is the conjugate base of NH₄⁺.

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Quick Revision Table

Topic	Key Point
Isoelectronic Species	Same number of electrons
CO₂	sp Hybridization
BF₃	Trigonal Planar
N₂	2 π Bonds
Internal Energy	State Function
Density	Intensive Property
NH₄⁺	Conjugate Base = NH₃
KClO₃	Cl Oxidation State = +5
BF₃	Lewis Acid
Carbon	Highest IE among Li, Be, B, C

Final Thoughts

Consistent practice of CSIR NET PYQs helps improve conceptual understanding and exam confidence. Focus on understanding the logic behind each answer rather than memorizing facts. Stay tuned for Part 3, where we will cover another set of important and easy-to-moderate level questions frequently asked in Chemical Sciences examinations.

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