Assertion (A) & Reason (B) MCQ

MCQ 11 Mark

Reason (R): RMgX on reaction with carbonyl compounds give alcohols.

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 21 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.

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MCQ 31 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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MCQ 41 Mark

Assertion $(A): \ce{(CH_3)_3 C-O-CH_3}$ gives $\ce{(CH_3)_3 C-I}$ and $\ce{CH_3OH}$ on treatment with $HI.$
Reason $(R):$ The reaction occurs by $S_N1$ 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 $A.$

$\ce{(CH_3)_3-C-O-CH_3}$ is an ether with two different alkyl groups, of which $\ce{(CH_3)_3-C-I,}$ tertiary alkyl group, on with hydrogen halide $(HI)$ forms a tertiary halide.
This occurs as the reaction is an $S_N1$ reaction. The reaction involves the formation of a stable carbocation. If the ether has a primary alkyl group, then the reaction follows the $S_N2$ mechanism.

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Chemistry Assertion (A) & Reason (B) MCQ

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