Answer:
The correct answer is 4 substracting hydride ions from olefins.
Step-by-step explanation:
The olefins are the unsaturated hydrocarbon also called alkenes that contain one double bond present between 2 carbon atoms.
On the other hand a carbenium ion is formed when a hydrocarbon loses a hydride ion to form a positively charged product.
For example allyl cation
CH2=CH-CH2+
The allyl cation is a carbenium ion formed by the removal of H- ion or hydride ion from the alkene propene.