Answer : The number of water molecules are, 7
Explanation :
The given unbalanced chemical reaction is,

First we have to separate into half reaction. The two half reactions are:


Now we have to balance the half reactions, we get
............(1)
........(2)
Now we have to balance the electrons of the half reactions. When we are multiplying the equation (1) by 2 and equation (2) by 5, we get


Now we have to add both the half reactions, we get the final balanced chemical reaction.

From the final balanced chemical reaction, we conclude that there are 7 number of water molecules present in this reaction on product side.
Hence, the number of water molecules are, 7