Answer:
The mole to mole ratio between oxygen gas and water is 2 : 1
Step-by-step explanation:
Balancing is making the number of atoms of each element same on both the sides (reactant and product side). 
To find the number of atoms of each element we multiply coefficient and the subscript 
For example 
 contains 
5 × 1 = 5 ,Ca atoms and 
5 × 2 = 10, Cl atoms 
If there is a bracket in the chemical formula 
For example 
 
we multiply coefficient × subscript × number outside the bracket to find the number of atoms 
(Please note: 3 is the coefficient, and if there is no number given then 1 will be the coefficient ) 
So 
3 × 3 = 9 , Ca atoms 
3 × 1 × 2 = 6, P atoms 
3 × 4 × 2 = 24, O atoms are present. 
So 
The balanced chemical equation is 

The number which stands in front of the chemical formula is the coefficient and it represents the number of moles of each substance. 
So we see here 2 is the coefficient of 
 and 1 is the coefficient of 
 
So the mole ratio of water and oxygen gas is 2 : 1 
(Answer)