Question

anyone plzz clear my doubt ....markownikov rule is happens only with Hbr but not with hcl and Hi​

Answer 1

In anti Markovnikov's addition by HBr in the presence of organic peroxide happens as it is a chain reaction. It is a free radical reaction in which all the steps of the reaction are exothermic , so we just need to initiate the reaction by providing suitable conditions then reaction will continue like a chain. It might also help you that Benzene is an important byproduct formed during this reaction.

In case of Chlorine and Iodine , this does not happen as one or more steps are endothermic, so it does not keep on going like a chain in the form of free radical reactions.