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JEE Chemistry

Chemistry questions for JEE Main — Physical, Organic, Inorganic Chemistry.

225 Q 5 Topics Take Test
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Difficulty: All Easy Medium Hard 171–180 of 225
Topics in JEE Chemistry
Q.171 Medium Organic Chemistry
The oxidation of primary alcohol to aldehyde can be selectively done using:
A KMnO4/acidic medium
B PCC (Pyridinium chlorochromate)
C Na2Cr2O7/H2SO4
D Dilute H2SO4 with heat
Correct Answer:  B. PCC (Pyridinium chlorochromate)
EXPLANATION

PCC oxidizes primary alcohols to aldehydes without further oxidation to carboxylic acids. KMnO4 and Na2Cr2O7 further oxidize aldehydes to carboxylic acids.

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Q.172 Medium Organic Chemistry
Which of the following compounds will show aldol condensation?
A Benzaldehyde
B Formaldehyde
C Acetaldehyde
D Chloroacetaldehyde
Correct Answer:  C. Acetaldehyde
EXPLANATION

Aldol condensation requires an α-hydrogen. Acetaldehyde has α-hydrogens and undergoes aldol condensation. Benzaldehyde and formaldehyde lack α-hydrogens.

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Q.173 Medium Organic Chemistry
In the Williamson ether synthesis, the reactivity of alkyl halides follows the order:
A Primary > Secondary > Tertiary
B Tertiary > Secondary > Primary
C Secondary > Primary > Tertiary
D Primary > Tertiary > Secondary
Correct Answer:  A. Primary > Secondary > Tertiary
EXPLANATION

Williamson ether synthesis follows SN2 mechanism, which is favored by primary alkyl halides due to minimal steric hindrance. Reactivity: Primary > Secondary > Tertiary.

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Q.174 Medium Physical Chemistry
A solution contains 0.1 M weak acid HA (Ka = 1×10⁻⁵). The degree of ionization is approximately:
A 0.01
B 0.001
C 0.1
D 0.0316
Correct Answer:  D. 0.0316
EXPLANATION

For weak acid: α = √(Ka/C) = √(1×10⁻⁵/0.1) = √(1×10⁻⁴) = 0.01 or 1%. Using exact formula: α ≈ 0.0316 (3.16%)

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Q.175 Medium Physical Chemistry
For the reaction 2A(g) ⇌ B(g) + C(g), if initial pressure is 2 atm and degree of dissociation is 0.5, what is the total pressure at equilibrium?
A 3 atm
B 2.5 atm
C 4 atm
D 1.5 atm
Correct Answer:  A. 3 atm
EXPLANATION

Initial: 2 atm of A. At equilibrium with α = 0.5: A dissociates to (1-0.5)×2 = 1 atm, producing B and C each at 0.5 atm. Total = 1 + 0.5 + 0.5 = 2 atm × (1 + α) = 2 × 1.5 = 3 atm

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Q.176 Medium Physical Chemistry
The molar conductivity of a weak electrolyte increases with dilution because:
A Conductivity of ions increases
B Degree of ionization increases
C Number of ions decreases
D Viscosity of solution increases
Correct Answer:  B. Degree of ionization increases
EXPLANATION

At higher dilutions, weak electrolytes ionize more completely, increasing degree of ionization and thus molar conductivity

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Q.177 Medium Physical Chemistry
For an exothermic reaction at 298 K, which condition favors spontaneity?
A ΔH > 0, ΔS > 0
B ΔH < 0, ΔS < 0
C ΔH < 0, ΔS > 0
D ΔH > 0, ΔS < 0
Correct Answer:  C. ΔH < 0, ΔS > 0
EXPLANATION

ΔG = ΔH - TΔS; For spontaneity ΔG < 0. Exothermic (ΔH < 0) with ΔS > 0 always gives ΔG < 0

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Q.178 Medium Physical Chemistry
The rate law for reaction is: rate = k[A]²[B]. If [A] is doubled and [B] is halved, how does rate change?
A Increases by 2 times
B Decreases by 2 times
C Remains same
D Increases by 4 times
Correct Answer:  A. Increases by 2 times
EXPLANATION

New rate = k(2[A])²(0.5[B]) = k × 4[A]² × 0.5[B] = 2k[A]²[B] = 2 × original rate

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Q.179 Medium Physical Chemistry
Which pair of substances will form an ideal solution?
A Ethanol and water
B Benzene and toluene
C Acetone and chloroform
D Acetic acid and water
Correct Answer:  B. Benzene and toluene
EXPLANATION

Benzene and toluene are both aromatic hydrocarbons with similar molecular structures, forming nearly ideal solutions

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Q.180 Medium Physical Chemistry
At 25°C, for a cell with E°cell = 0.92 V, what is ΔG°? (F = 96485 C/mol)
A -88.8 kJ/mol
B -177.6 kJ/mol
C -44.4 kJ/mol
D -266.4 kJ/mol
Correct Answer:  B. -177.6 kJ/mol
EXPLANATION

ΔG° = -nFE°; For bivalent ion transfer: ΔG° = -2 × 96485 × 0.92 ≈ -177.6 kJ/mol

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