Electrophilic addition reactions proceed in two steps. The first step involves the addition of an electrophile. Name the type of intermediate formed in the first step of the following addition reaction.

H₃ C—HC = CH₂ + H⁺ →?

Correct answer: 3)

Concept:

• Electrophilic addition reactions are those in which the electrophile attacks on the unsaturated bond.
• That’s why a compound must have a double or triple bond to undergo electrophilic addition reaction.
• Because of the presence of >C = C< bond in molecules, alkenes generally take part in the addition reactions. 
• Markovnikoff's Rule: First Rule : When molecule of a HX add up on unsymmetrical unsaturated hydrocarbon, the halogen atom goes to the unsaturated carbon atom bearing lesser number of hydrogen atoms.
•  Second Rule : In the addition of HX to vinyl halide and analogous compounds, the halogen attaches itself to the carbon atom, on which the halogen atom is already present. 

Explanation:

• When electrophile H⁺ attacks on H3 C—HC =CH2  delocalization of electron can takes place in two possible way:

• As 2^o carbocation is more stable than 1^o carbocation thus second addition is more feasible.
• Stability of carbocation is the basis of Markownikoff's rule.

Conclusion:

Thus, 2∘ carbocation is  an intermediate formed in the first step of the given addition reaction.