<Tr> <Th> imperial / US units </Th> <Td> 2.08 × 10 in </Td> </Tr> <Tr> <Th> natural units </Th> <Td> 7015167272458542827 ♠ 2.68 × 10 / eV 7024327000000000000 ♠ 3.27 × 10 l </Td> </Tr> <P> The Bohr radius (a or r) is a physical constant, approximately equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state . It is named after Niels Bohr, due to its role in the Bohr model of an atom . Its value is 6989529177210670000 ♠ 5.291 772 1067 (12) × 10 m . </P> <P> In SI units the Bohr radius is: </P>

What is the radius of the hydrogen atom