Sports trainers treat sprains and soreness with ethyl bromide. it is manufactured by reacting ethylene with hydrogen bromide:

Trainers use this substance because the reaction of the product on the skin is an exothermic one. This produces a feeling of warmth and heat. Heating an injury like a sprain with warmth or heat increases blood flow to the area and promotes healing as the flow of blood carries the necessary substances for healing. 

Do u have the n? or maybe the m?

The answer is b i think