Question

Directions: Each of these questions contains an Assertion followed by a reason. Read them carefully and answer the question on the basis of the following options. You have to select the best describes the two statements.

Question statement:

Assertion: Propene reacts with $\mathrm{HBr}$ to give isopropyl bromide.

Reason: Addition of ${\mathrm{Br}}_2$ to alkene takes place faster in presence of an ionizing substance

• A. If both Assertion and Reason are correct and Reason is the correct explanation of Assertion
• B. If both Assertion and Reason are correct and Reason is not the correct explanation of Assertion
• C. If Assertion is correct but Reason is incorrect.
• D. If Assertion is incorrect but Reason is correct.

Answer 1

The correct option is B

If both Assertion and Reason are correct and Reason is not the correct explanation of Assertion

The explanation for the correct option:

(B)

Assertion: Markownikoff's rule applies to unsymmetrical reagents like $\mathrm{HX},{\mathrm{H}}_2\mathrm{O}\mathrm{and}\mathrm{HOX}$ reacting with unsymmetrical alkenes.

Example: Propene reacts with $\mathrm{HBr}$ to give isopropyl bromide.

${\mathrm{CH}}_3\mathrm{CH}={\mathrm{CH}}_2\left(\mathrm{g}\right)+\mathrm{HBr}\left(\mathrm{aq}\right)\to {\mathrm{CH}}_3\mathrm{CH}\left(\mathrm{Br}\right){\mathrm{CH}}_3\left(\mathrm{l}\right)$

The negative part of the adding molecule (unsymmetrical reagent) goes to the carbon atom of the double bond with the least number of $\mathrm{H}-$atoms, according to the rule.

Markownikoff's rule governs the addition of an unsymmetrical added molecule or unsymmetrical alkene. The attacking molecule's negative portion attaches to a less hydrogenated carbon atom.

Reason: The reason is incorrect because the rate of addition of ${\mathrm{Br}}_2$ to alkenes increases in the presence of an organic solvent, such as carbon tetrachloride $\left({\mathrm{CCl}}_4\right)$, or in the presence of covalent or ionic molecules. Therefore, the reason is false.

Thus, both Assertion and Reason are correct and Reason is not the correct explanation for Assertion

Hence, the correct answer is option (B).