By using ratio, it is obtained that if there are 8 atoms of hydrogen, there are 4 atoms of oxygen.
What is ratio?
Ratio is used to find a comparision between two quantities with the same unit
The first part of the ratio is called antecedant and the second part of the ratio is called consequent.
Here,
In a molecule of water, there are 2 atoms of hydrogen and 1 atom of oxygen
Ratio of hydrogen and oxygen = 2 : 1
Number of atoms of hydrogen = 8
Let the number of hydrogen atom be 2x and number of oxygen atom be x
By the problem,
Number of oxygen atom = 4
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