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Chemistry Assertion (A) & Reason (B) MCQ [1M]

MODEL PAPER 8 · Bihar Board (BSEB) STD 12 Science (BSEB - English Medium). 4 questions.

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Assertion (A) & Reason (B) MCQ [1M]

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4 questions · timed · auto-graded

MCQ 11 Mark
Assertion (A): (CH3)3 C-O-CH3 gives (CH3)3 C-I and CH3OH on treatment with HI.
Reason (R): The reaction occurs by SN1 mechanism.
  • ✓
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
Correct option: A.
Both A and R are true and R is the correct explanation of A.
(a) Both A and R are true and R is the correct explanation of A.
Explanation: (CH3)3-C-O-CH3 is an ether with two different alkyl groups, of which (CH3)3-C-I, tertiary alkyl group, on with hydrogen halide (HI) forms a tertiary halide.
This occurs as the reaction is an SN1 reaction. The reaction involves the formation of a stable carbocation. If the ether has a primary alkyl group, then the reaction follows the SN2 mechanism.
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MCQ 21 Mark
  • A
    Both A and R are true and R is the correct explanation of A.
  • ✓
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
Correct option: B.
Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
Explanation: Both A and R are true but R is not the correct explanation of A.
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MCQ 31 Mark
Assertion (A): A solution of sucrose in water is dextrorotatory but on hydrolysis in presence of little hydrochloric acid it becomes laevorotatory.
Reason (R): Sucrose on hydrolysis gives unequal amounts of glucose and fructose as a result of which change in sign of rotation is observed.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • ✓
    A is true but R is false.
  • D
    A is false but R is true.
Answer
Correct option: C.
A is true but R is false.
(c) A is true but R is false.
Explanation: A is true but R is false.
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MCQ 41 Mark
Assertion (A): Di-tert-butyl ether cannot be prepared by Williamson's synthesis.
Reason (R): tert-Butyl bromide on treatment with sodium lert-butoxide preferentially undergoes elimination to form isobutylene and rert-butyl alcohol.
  • ✓
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
Correct option: A.
Both A and R are true and R is the correct explanation of A.
(a) Both A and R are true and R is the correct explanation of A.
Explanation: Williamson's synthesis is not applicable to tert. alkyl halides because alkoxide ions being both powerful nucleophiles and bases would bring dehydro-halogenation of the tert. alkyl halides to form alkenes preferentially.
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Assertion (A) & Reason (B) MCQ [1M] - Chemistry STD 12 Science Questions - Vidyadip