<u>Answer:</u> The number of iron atoms in given amount is 
<u>Explanation:</u>
Density of a substance is defined as the ratio of its mass and volume. The chemical equation representing density of a substance is:

We are given:
Density of iron = 
Volume of iron = 
Putting values in above equation, we get:

To calculate the number of moles, we use the equation:

Given mass of iron = 7.87 g
Molar mass of iron = 55.65 g/mol
Putting values in above equation, we get:

According to mole concept:
1 mole of an element contains
number of atoms.
So, 0.141 moles of iron will contain =
number of atoms.
Hence, the number of iron atoms in given amount is 