I had the same question, it's most likely B.
Answer:
119.85 grams Br or 120. grams Br (sig figs)
Explanation:
1.50 moles Br 79.90 g Br
--------------------- x ------------------------ = 119.85 grams Br or 120 grams Br (sig figs)
1 mole
Use the formula for second order reaction:

C = concentration at time t
C0 = initial conc.
k = rate constant
t = time
1st equation :

2nd Equation:

Find

from 1st equation and put it in 2nd equation:


k = 0.046