Which Coefficient Should Be Placed in Front of the H₂O $\rightarrow$

Which coefficient should be placed in front of the H₂O when balancing the following equation?
(NH₄) ₂Cr₂O_7(s) $\rightarrow$ Cr₂O_3(s) + N_2(g) + H₂O_(g)

A) 1
B) 2
C) 3
D) 4
E) 8