Option 2: BCC
The expression for density of cell is as follows:
...... (1)
Here, n is number of atom per unit cell, A is atomic mass, is volume of crystal and is Avagadro's number.
Also, the expression for volume of crystal is as follows:
The atomic weight, density and Radius of atom is given 43.1 g/mol, and 0.122 nm respectively.
Converting radius into cm:
Thus,
Putting the value to calculate volume first:
Now, putting all the values in equation (1)
On rearranging,
The number of atom per unit cell is 2 for body centered cubic lattice thus, correct option is BCC.