Letter It is). It could not be the letters b and c because the conditions that the exercise brings up on the arrows in the scheme are conditions that characterize addition and not substitution reactions. It’s the letter It is because we can see that the pair is between a carbon with one hydrogen and another with two, so in product A the OH of the water goes to the one that has a hydrogen (number 2) and in product B the Cl too, because according to Markovnikov’s rule, these groups are added to the carbon with the least hydrogen in the pair.