The atomic mass of carbon is 12 g and that of oxygen is 16 g. How many grams of carbon contains as many atoms as 100 g of oxygen?

Given mass of oxygen = 100 g
Gram atomic mass of carbon = 12 g
Gram atomic mass of oxygen = 16 g

Let the required mass of carbon be $x$ grams.
Number of atoms of carbon = number of atoms of oxygen.

Number of atoms = $\frac{\text{Mass of element}}{\text{Gram atomic mass}}\times \text{Avogadro's number}$ [1 Mark]
$\therefore$ $\frac{x}{12}\times 6.022\times {10}^{23}=\frac{100}{16}\times 6.022\times {10}^{23}$
[1 Mark]
$\Rightarrow x=\frac{100\times 12}{16}=75$

Hence, 75 grams of carbon contains as many atoms as 100 g of oxygen. [1 Mark]