Draw the major organic product from reaction of 1-butyne with 1 equiv br2. specify stereochemistry when it is relevant. in cases where there is more than one answer, just draw one. do not draw inorganic by-products. if no reaction occurs, draw the organic starting material.

Following shows the reaction when 1-butyne is reacted with 1 equivalent of Bromine. This is electrophillic addition reaction. Trans configuration is the product because the incoming bromide can only attack on the backside of the bromirenium Ion, Hence giving a trans configuration. The reaction is shown below,

Well to my expert knowledge and my exquisite calculations i think the the negative ion # 412 is the key to sucess