Order of magnitude

“Order of magnitude” asks for the approximate scale, not an exact measurement for every atom or molecule.

If asked for the order of magnitude, give $10^{-10}\,\text{m}$; if asked for the typical size, write approximately $1 \times 10^{-10}\,\text{m}$.

An order of magnitude is a power of ten: give the typical size of an atom or small molecule as about $10^{-10}\,\text{m}$, not simply as “very small”.