Question

Which of the following has the maximum number of atoms of oxygen?
A. $10ml{\text{ of }}{H_2}O(l)$
B. $0.1mole{\text{ of }}{V_2}{O_5}$
C. $12g{\text{ }}{O_3}(g)$
D. $12.044 \times {10^{23}}{\text{ molecules of }}C{O_2}$

Answer 1

The basic method of comparison of the number of oxygen atoms in various compounds can be based on the number of moles of oxygen atoms present in the different volumes, weights and number of molecules given. The greater the number of moles, greater will be the number of atoms.

Complete answer:
At standard temperature and pressure, each gas is known to contain a fixed volume for one mole of it. Thus, one mole of water must contain a volume of $22.4L$ or $22400ml$ . But only $10ml$ of water is available. Since there is a single oxygen atom in the chemical formula of water, the amount of oxygen atoms present in one mole of water is also one.
The moles of water can be calculated by dividing its given volume by the volume present in one mole.
$moles({H_2}O) = \dfrac{{10ml}}{{22400ml}} = 0.000446moles$
Thus, $0.000446moles$ of oxygen atoms are present $10ml$ of water.
Vanadium pentoxide contains five moles of oxygen atoms per mole of the compound. Therefore the number of moles of oxygen atoms present in $0.1$ mole is :
$moles(O) = 0.1 \times 5 = 0.5moles$
The number of moles of ozone molecules in $12g$ of ozone is :
$moles({O_3}) = \dfrac{{12}}{{48}} = 0.25moles$
And each mole of ozone contains three moles of oxygen atom, therefore the number of moles of oxygen atoms present in $12g$ of ozone is:
$moles(O) = 0.25moles \times 3 = 0.75moles$
Each mole contains $6.022 \times {10^{23}}$ molecules of any compound. Thus there are two moles of atoms present in $12.044 \times {10^{23}}$ molecules of carbon dioxide.
Each mole of carbon dioxide contains two moles of oxygen atoms, therefore the moles of oxygen atoms in carbon dioxide are:
$moles(O) = 2 \times 2moles = 4moles$

Thus, the maximum number of oxygen atoms are present in $12.044 \times {10^{23}}$ molecules of carbon dioxide and option (d) is correct.

Note:
The mole concept is used in this question as it finds a relationship between the molar masses, the number of constituent atoms or molecules and the volumes associated with different substances. Thus a standard method of comparison of amounts is always done with the help of moles.