Which of the following best describes Markovnikov's rule?

Markovnikov's rule states that when a hydrogen halide (like HBr or HCl) adds to an asymmetrical alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen substituents, which effectively means the less substituted carbon of the double bond. This leads to the formation of a more stable carbocation intermediate during the reaction. Therefore, when the addition of the hydrogen halide occurs, the more stable product, which often results from the more substituted carbon, will predominate.

The idea behind this is rooted in carbocation stability: tertiary carbocations are more stable than secondary ones, which in turn are more stable than primary. Hence, the preference for the hydrogen to bond with the carbon that already has more hydrogen atoms maximizes the stability of the resulting carbocation and the product formed. This understanding is critical in predicting the outcome of reactions involving unsymmetrical alkenes.

The other choices do not accurately reflect the principle of Markovnikov's rule. The statement regarding the hydrogen atom attaching to the less substituted carbon describes the opposite of what occurs according to the rule, while the assertion about the carbon-carbon double bond not reacting with hydrogen halides is incorrect since such reactions are fundamental to addition mechanisms.