The most contributing structure is bromoethyne which has a triple bond between the two carbons, a hydrogen bonded to one carbon and a bromine to the other. In this compound. There are 4 valence electrons contributed by each carbon (8 for both), 1 from the hydrogen and 7 from the bromine. This gives a total of 16. There are 2 electrons involved in each bond: 6 in the CC triple bond, 2 in the CH bond and 2 in CBr bond. That is 10 bonding electrons which means that there are 6 remaining electrons. Both carbons and the hydrogen have a filled valence shell while the Bromine requires 6 more electrons to complete its shell. So the 6 remaining electrons are found around bromine as lone pairs. 6 lone electrons = 3 lone pairs.
There are 4 lone pairs in the C2HBr compound.
There are 16 valence electrons total in this compound, and the carbons and bromine want a full octet.
Since there are only 16, there is a long pair on both carbons and 2 lone pairs on bromine.