Question

Ratio of hydrogen to oxygen in water is:
A. 2:1
B. 1:2
C. 7:1
D. 8:1

Answer 1

Hint: Water is formed from two hydrogen atoms and one oxygen atom. Ratio of hydrogen to oxygen means number of hydrogen atoms divided by number of oxygen atoms.

Complete step by step answer:
Here, we know that water molecules contain two hydrogen atoms and one oxygen atom. We can understand this like that, if we combine one atom and two hydrogen atoms then it will form one water molecule. And also we can understand this by acid-base reaction (neutralization reaction), like if one \[O{{H}^{-}}\]ion combine with one \[{{H}^{+}}\] ion then it will form one water molecule that is \[{{H}_{_{2}}}O\].
So, the ratio of hydrogen to oxygen means the number of hydrogen atoms divided by the number of oxygen atoms.
If we take one mole of water then it will contain $6.03 \times 10^{23}$ water molecules.
And here mole is the SI unit for the amount of a substance and $6.02 \times 10^{23}$ is the Avogadro number. In water two hydrogen atoms form a single bond with hydrogen.
So,
Ratio of hydrogen to oxygen in water = $\dfrac{\text{number of hydrogen atoms}}{\text{number of oxygen atoms}} = \dfrac{2}{1}$
= 2:1
So, the answer is “A”.

Note: Here are chances that you get confused with the term “ratio of hydrogen to the oxygen” or “ratio of oxygen to the hydrogen”, because it will change your answer. So, be careful about this term.