What’s the answer to this science problem?

The image is not accurate because

the heavier atoms are moving faster than the lighter ones

but the lighter ones must move faster than the heavier ones.

Explanation:

The image depicts the atoms of two different elements; atoms of lighter and heavier elements.

And the rate of diffusion (movement of atoms) of an element is inversely proportional to the square root of its molecular.

⇒ As the weight increases, the rate of diffusion (movement of atoms) decreases.

And as the weight decreases, the rate of diffusion (movement of atoms) increases.

so, heavier atoms move slowly compared to lighter atoms.

The image is not accurate because

the heavier atoms are moving faster than the lighter ones

but the lighter ones must move faster than the heavier ones.