Answer:
a)
is the average volume required for each iron atom.
b) The distance between the centers of adjacent atoms is
.
Explanation:
a) Mass of an iron = 7.84
Volume of iron = 
Let the x atoms of iron weights 7.84 g and volume of
.
Mass of an iron atom = 


Volume of x atoms of iron = 
Volume of an iron atom = v




is the average volume required for each iron atom.
b) Volume of an iron atom = v
Volume of the cube = 
Length of iron cube -= s


According to question we are treating iron atom as cube. So all the cubic iron atoms will have a same side.

The distance between the centers of adjacent atoms:
Horizontal distance of the center from the one face of the cubic iron atom:
=
Horizontal distance of the center from the one face of the another cubic iron atom:
=

The distance between the centers of adjacent atoms is
.