The theoretical proportion is given by the balanced chemical equation:
2 mol NBr / 3 mol Na OH
Then x mol NaOH / 40 mol NBr3 = 3mol NaOH/2 mol NBr3
Solve for x, x = 40 * 3/2 = 60 mol NaOH.
Given that there are 48 mol NaOH (less than 60) this is the limitant reactant and the other is the excess reactant.
Answer: NBr3..