The intermediate formed during the addition of HClHCl to propene in the presence of peroxide is

The intermediate formed during the addition of HCl to propene in the presence of peroxide is a carbocation. Here are the steps:

1. The reaction begins with the formation of a free radical on the chlorine atom due to the presence of peroxide. Peroxide is a radical initiator that can break the H-Cl bond homolytically to form two chlorine radicals.

2. The chlorine radical then reacts with the propene molecule. It will preferentially add to the less substituted carbon atom due to its size and reactivity, forming a secondary carbocation. This is known as the Markovnikov rule.

3. Finally, the remaining Cl- ion will react with the carbocation, forming the final product.

So, the intermediate in this reaction is a secondary carbocation.