To calculate the volume of a simple cubic unit cell composed of atoms with a radius of 2.5 angstroms, we start by recalling that the volume of a cube is given by the formula:

V = a³

where V is the volume and a is the edge length of the cube. For a simple cubic unit cell, the edge length a is twice the radius of the atom:

a = 2r

Given that the radius r is 2.5 angstroms, we first convert this radius into centimeters. The conversion factor is:

1 \text{ angstrom} = 10^{-10} \text{ meters} = 10^{-8} \text{ centimeters}

Thus, the radius in centimeters is:

r = 2.5 \times 10^{-8} \text{ cm}

Now, we can calculate the edge length:

a = 2 \times r = 2 \times (2.5 \times 10^{-8}) = 5.0 \times 10^{-8} \text{ cm}

Next, we cube the edge length to find the volume:

V = (5.0 \times 10^{-8})^3 = 1.25 \times 10^{-23} \text{ cm}^3

Therefore, the volume of the simple cubic unit cell is:

V \approx 1.3 \times 10^{-22} \text{ cm}^3