The reaction of propene with HOCl proceeds via the addition of:
(A) H+
in first step
(B) Cl+
in the first step
(C) HO−
in first step
(D) Cl+
and HO−
in the first step

To understand the reaction of propene (an alkene) with hypochlorous acid (HOCl), we should analyze the mechanism of the reaction.

Step 1: Identify the Reaction
The reaction between propene and HOCl involves the addition of HOCl across the double bond of propene.

Step 2: Mechanism of Addition
Formation of a Carbocation:

When propene reacts with HOCl, the double bond of propene acts as a nucleophile and attacks the hydrogen atom of HOCl.
This step leads to the formation of a carbocation intermediate and the release of a chloride ion (Cl⁻).
Nucleophilic Attack by Chloride Ion:

The Cl⁻ ion, produced in the previous step, can now attack the carbocation.
This results in the formation of a chlorohydrin product.
Step 3: Determine the Correct Answer
In the first step of the reaction, the proton (H⁺) from HOCl adds to the double bond of propene, leading to the formation of a carbocation.
Therefore, the correct choice is (A) H⁺ in the first step.
Summary
The reaction of propene with HOCl proceeds via the addition of H⁺ in the first step, leading to a carbocation intermediate, which then reacts with Cl⁻ to form the final product.

Final Answer
(A) H⁺ in the first step.