The size of an atomic nucleus can be understood in terms of its radius, though it's important to note that nuclei are not always perfectly spherical. The radius, $ R $, of a nucleus is often given by the formula $ R = R_0 A^{1/3} $, where $ R_0 $ is a constant approximately equal to $ 1.2 \times 10^{-15} $ meters (or $ 1.2 \times 10^{-13} $ cm) and $ A $ is the mass number of the atom (which represents the total number of protons and neutrons in the nucleus).

Based on this formula, we can see that the order of magnitude for the size of a nucleus is indeed very small. The given options are:

• Option A: $ 10^{-10} $ cm
• Option B: $ 10^{-13} $ cm
• Option C: $ 10^{-15} $ cm
• Option D: $ 10^{-8} $ cm

The radius of an atomic nucleus is closest to Option B: $ 10^{-13} $ cm, considering the conversion from $ 1.2 \times 10^{-15} $ meters to centimeters. While $ 10^{-15} $ meters (or femtometers/fm) is a commonly used unit to describe the scale of nuclear radii directly, when converted to centimeters, the scale of $ 10^{-13} $ cm fits the description of the size of an atomic nucleus closer than the other options provided.