Among the following, the reaction that proceeds through an electrophilic substitution, is :

An alkene “A” on reaction with O₃ and Zn + H₂O gives propanone and ethanal in equimolar ratio. Addition of HCl to alkene “A” gives “B” as the major product. The structure of product “B” is :

The most suitable reagent for the following conversion, is :

Hydrocarbon (A) reacts with bromine by substitution to form an alkyl bromide which by Wurtz reaction is converted to gaseous hydrocarbon containing less than four carbon atoms. (A) is