We know that
#"1 C atom = 12 u"#
and
#6.022 × 10^23color(white)(l) "C atoms" = "12 g"#
∴ #"1 u" = 1 color(red)(cancel(color(black)("u"))) × (1 color(red)(cancel(color(black)("C atom"))))/(color(red)(cancel(color(black)(12))) color(red)(cancel(color(black)("u")))) × (color(red)(cancel(color(black)(12))) "g")/(6.022 × 10^23 color(red)(cancel(color(black)("C atoms")))) = 1.661 × 10^"-24"color(white)(l) "g"#