CSIR NET Chemical Sciences 2024–2025 PYQs with Detailed Solutions (Part 2)
The magnetic moment (spin-only) of a d³ ion is: (CSIR NET Chemical Sciences – June 2024)
d³ அயனின் spin-only காந்தத் திருப்புத்திறன் (magnetic moment) என்ன?
A) 1.73 BM
B) 2.83 BM
C) 3.87 BM
D) 4.90 BM
Answer: ✅ C) 3.87 BM
Detailed Solution: For a d³ ion, the number of unpaired electrons (n) is 3. Spin-only magnetic moment is given by μ = √[n(n+2)] BM. Therefore, μ = √[3(3+2)] = √15 = 3.87 BM. Hence, the correct answer is C.
Which of the following has the highest electronegativity? (CSIR NET Chemical Sciences – December 2024)
பின்வருவனவற்றில் அதிக மின்எதிர்மறைத்தன்மை (electronegativity) உடையது எது?
A) Oxygen
B) Nitrogen
C) Fluorine
D) Chlorine
Answer: ✅ C) Fluorine
Detailed Solution: Electronegativity increases across a period and decreases down a group. Fluorine is the most electronegative element in the periodic table with a Pauling value of 3.98. Therefore, fluorine has the highest electronegativity.
The number of σ bonds in ethyne (C₂H₂) is: (CSIR NET Chemical Sciences – June 2024)
எத்தைன் (C₂H₂) மூலக்கூறில் உள்ள σ பிணைப்புகளின் எண்ணிக்கை என்ன?
A) 2
B) 3
C) 4
D) 5
Answer: ✅ B) 3
Detailed Solution: Ethyne has the structure H−C≡C−H. The C≡C triple bond contains one σ bond and two π bonds. Additionally, there are two C−H σ bonds. Therefore, total σ bonds = 1 + 2 = 3.
Which of the following is diamagnetic? (CSIR NET Chemical Sciences – December 2024)
பின்வருவனவற்றில் diamagnetic தன்மை உடையது எது?
A) O₂
B) NO
C) N₂
D) O₂⁻
Answer: ✅ C) N₂
Detailed Solution: Diamagnetic substances contain all paired electrons. N₂ has all electrons paired in its molecular orbital configuration. Therefore, N₂ is diamagnetic, whereas O₂, NO, and O₂⁻ are paramagnetic.
The coordination number of Ni in [Ni(CO)₄] is: (CSIR NET Chemical Sciences – June 2025)
[Ni(CO)₄] சேர்மத்தில் Ni-இன் coordination number என்ன?
A) 2
B) 3
C) 4
D) 6
Answer: ✅ C) 4
Detailed Solution: Coordination number is the number of donor atoms directly attached to the central metal atom. In [Ni(CO)₄], four CO ligands are attached to Ni. Therefore, coordination number = 4.
Which gas is responsible for the greenhouse effect to the greatest extent among the following? (CSIR NET Chemical Sciences – December 2024)
பின்வரும் வாயுக்களில் greenhouse effect-க்கு முக்கிய காரணமானது எது?
A) H₂
B) CO₂
C) O₂
D) N₂
Answer: ✅ B) CO₂
Detailed Solution: Carbon dioxide absorbs infrared radiation emitted from the Earth's surface and contributes significantly to global warming and the greenhouse effect. Therefore, CO₂ is the correct answer.
The shape of SF₆ molecule is: (CSIR NET Chemical Sciences – June 2025)
SF₆ மூலக்கூறின் வடிவம் என்ன?
A) Tetrahedral
B) Square Planar
C) Octahedral
D) Trigonal Bipyramidal
Answer: ✅ C) Octahedral
Detailed Solution: Sulfur in SF₆ forms six bonds with fluorine atoms and has no lone pairs. According to VSEPR theory, six bond pairs arrange themselves in an octahedral geometry.
Which of the following is a strong electrolyte? (CSIR NET Chemical Sciences – December 2024)
பின்வருவனவற்றில் வலுவான மின்பகுப்பு (strong electrolyte) எது?
A) CH₃COOH
B) NH₄OH
C) HCl
D) Urea
Answer: ✅ C) HCl
Detailed Solution: HCl completely ionizes in aqueous solution, producing H⁺ and Cl⁻ ions. Therefore, it is a strong electrolyte. Acetic acid and ammonium hydroxide are weak electrolytes.
The oxidation number of sulfur in H₂SO₄ is: (CSIR NET Chemical Sciences – June 2024)
H₂SO₄ இல் கந்தகத்தின் (Sulfur) ஆக்சிடேஷன் எண் என்ன?
A) +4
B) +5
C) +6
D) +7
Answer: ✅ C) +6
Detailed Solution: Let oxidation state of sulfur be x. 2(+1) + x + 4(−2) = 0. Therefore, 2 + x − 8 = 0. Hence, x = +6.
The IUPAC name of CH₃COOH is: (CSIR NET Chemical Sciences – February 2025)
CH₃COOH சேர்மத்தின் IUPAC பெயர் என்ன?
A) Methanoic acid
B) Ethanoic acid
C) Propanoic acid
D) Ethanol
Answer: ✅ B) Ethanoic acid
Detailed Solution: CH₃COOH contains two carbon atoms and a carboxylic acid functional group. Therefore, its IUPAC name is Ethanoic acid.
Which quantum number specifies the orientation of an orbital? (CSIR NET Chemical Sciences – June 2025)
ஒரு ஆர்பிட்டலின் திசையை (orientation) குறிப்பிடும் quantum number எது?
A) Principal quantum number
B) Azimuthal quantum number
C) Magnetic quantum number
D) Spin quantum number
Answer: ✅ C) Magnetic quantum number
Detailed Solution: The magnetic quantum number (mₗ) specifies the orientation of an orbital in space. Principal quantum number determines size, azimuthal quantum number determines shape, and spin quantum number determines electron spin.
The bond angle in NH₃ is approximately: (CSIR NET Chemical Sciences – December 2024)
NH₃ மூலக்கூறின் பிணைப்பு கோணம் (bond angle) சுமார் எவ்வளவு?
A) 90°
B) 107°
C) 109.5°
D) 120°
Answer: ✅ B) 107°
Detailed Solution: NH₃ is sp³ hybridized with one lone pair. Lone pair-bond pair repulsion decreases the bond angle from 109.5° to approximately 107°.
Which of the following is an alkaline earth metal? (CSIR NET Chemical Sciences – June 2025)
பின்வருவனவற்றில் alkaline earth metal எது?
A) Sodium
B) Potassium
C) Calcium
D) Aluminium
Answer: ✅ C) Calcium
Detailed Solution: Alkaline earth metals belong to Group 2 of the periodic table. Calcium is a Group 2 element and therefore an alkaline earth metal.
The molecular formula of benzene is: (CSIR NET Chemical Sciences – December 2024)
பென்சீனின் (Benzene) மூலக்கூறு வாய்ப்பாடு என்ன?
A) C₆H₆
B) C₆H₁₂
C) C₅H₆
D) C₇H₈
Answer: ✅ A) C₆H₆
Detailed Solution: Benzene is an aromatic hydrocarbon containing six carbon atoms arranged in a ring with six hydrogen atoms attached. Therefore, its molecular formula is C₆H₆.
Which of the following is a noble gas? (CSIR NET Chemical Sciences – June 2025)
பின்வருவனவற்றில் noble gas எது?
A) Nitrogen
B) Oxygen
C) Helium
D) Hydrogen
Answer: ✅ C) Helium
Detailed Solution: Helium belongs to Group 18 of the periodic table. Group 18 elements are known as noble gases because they possess completely filled valence shells.
The hybridization of BeCl₂ in gaseous state is: (CSIR NET Chemical Sciences – December 2024)
வாயு நிலையில் BeCl₂-ன் hybridization என்ன?
A) sp
B) sp²
C) sp³
D) dsp²
Answer: ✅ A) sp
Detailed Solution: In gaseous BeCl₂, the central Be atom forms two sigma bonds and has no lone pairs. Therefore, it undergoes sp hybridization and exhibits a linear geometry.
Which law states that equal volumes of gases contain equal numbers of molecules at the same temperature and pressure? (CSIR NET Chemical Sciences – June 2025)
ஒரே வெப்பநிலை மற்றும் அழுத்தத்தில் சம அளவு வாயுக்கள் சம எண்ணிக்கையிலான மூலக்கூறுகளை கொண்டிருக்கும் என்று கூறும் விதி எது?
A) Boyle's Law
B) Charles Law
C) Avogadro's Law
D) Graham's Law
Answer: ✅ C) Avogadro's Law
Detailed Solution: Avogadro's law states that equal volumes of all gases under identical conditions of temperature and pressure contain equal numbers of molecules.
Which of the following is a reducing agent? (CSIR NET Chemical Sciences – February 2025)
பின்வருவனவற்றில் reducing agent எது?
A) KMnO₄
B) K₂Cr₂O₇
C) H₂
D) O₃
Answer: ✅ C) H₂
Detailed Solution: Hydrogen donates electrons and reduces many metal oxides to metals. Therefore, it acts as a reducing agent. KMnO₄, K₂Cr₂O₇, and O₃ are oxidizing agents.
The atomic number of carbon is: (CSIR NET Chemical Sciences – December 2024)
கார்பனின் அணு எண் (Atomic Number) என்ன?
A) 4
B) 5
C) 6
D) 7
Answer: ✅ C) 6
Detailed Solution: Carbon contains six protons in its nucleus. Atomic number is defined as the number of protons present in the nucleus. Therefore, the atomic number of carbon is 6.
Which of the following molecules is linear? (CSIR NET Chemical Sciences – June 2025)
பின்வரும் மூலக்கூறுகளில் நேர்கோட்டு (linear) வடிவம் உடையது எது?
A) NH₃
B) H₂O
C) CO₂
D) BF₃
Answer: ✅ C) CO₂
Detailed Solution: In CO₂, the central carbon atom is sp hybridized and forms two double bonds with oxygen atoms. The two electron domains arrange themselves 180° apart, resulting in a linear geometry. Therefore, CO₂ is linear.
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