The least amount of energy required to activate atoms or molecules to a state in which they can undergo a chemical reaction.
A displacement reaction will occur from the system given above. The chlorine molecules will displace the bromide ions in the solution of sodium bromide. The reaction will yield to sodium chloride and bromine. The reaction will be:
2NaBr + Cl2 = 2NaCl + Br2
To determine whether the amount of H2 in the lab is dangerous, we first need to know how much hydrogen gas is present in the room in units of percent by volume. For this particular problem, we cannot exactly determine since we do not know the total volume of the room. Hope this answers the question.