how can we choose a reaction that has gone markoniff rule or anti-markonic rule as there would be change in the direction of the species to attack

Markovnikov's Rule:

 

In case of Markovnikov's rule, the addition of halogen halides to alkenes is an electrophilic addition reaction.

 

 

 

 

 

Since a 2⁰  carbocation(I) is more stable than 1⁰ carbocation(II), therefore carbocation(I) is predominantly formed.

 Markovnikov's addition occurs through the more stable carbocation intermediate.

 

Peroxide effect :

 

Peroxide effect is observed only with HBr and not with HF,HCl, or HI