In what unit is atomic radius expressed, defined as the distance between the nucleus and the outermost shell?

1. Atomic radius measures atomic size as a distance. 2. It is expressed in picometre (pm), where $1\,\text{pm} = 10^{-12}\,\text{m}$. 3. This unit is smaller than a nanometre. 4. Rule out C and D: gram and mole measure mass and amount, not length. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 2 "Periodic Classification of Elements", p.34_