In the addition of hbr to 1-butyne the electrophile in the first step of the mechanism is

            In the addition of hbr to 1-butyne the electrophile in the first step of the mechanism is Hydrogen atom of HBr.

Explanation:
                   In this reaction first of all HBr approaches the triple bond. A Pi Complex (weak inter-molecular interactions) is formed between the two molecules. And the triple bond attacks the partial positive hydrogen atom creating a negative charge on Bromine along with positive charge on itself (Sigma Complex). In second step the negative Bromide attacks the positive carbon of Butyne.

7is b8 is d9 is c10 is a11 is d

Okay well gravitational energy is matter forced by gravity making energy though the kinetic energy then the electric energy produces electricity from the kinetic energy and the kinetic energy gets its energy from the gravitational energy. was that the answer you wanted or something else?