Answer :
C
A has 2H 2O on the left and 4H 2O on the right
B has 4H 4O on the left and 4H 2O on the right
D has 2H 2O on the left and 2H 4O on the right
C has 2H 2O and 2H 2O so is balanced.
A has 2H 2O on the left and 4H 2O on the right
B has 4H 4O on the left and 4H 2O on the right
D has 2H 2O on the left and 2H 4O on the right
C has 2H 2O and 2H 2O so is balanced.