Answer is: a line containin 7,7e15 cm.
gr(Cu) = 128 pm = 128e-12 m · 10² cm/1 m = 1,28e-8 cm.
n(Cu) = 1 mol.
Na = 6,022e23 1/mol; Avogadro number.
N(Cu) = n(Cu) · Na.
N(Cu) = 1 mol · 6,022e23 1/mol.
N(Cu) = 6,022e23.
l = r(Cu) · N(Cu).
l = 1,28e-8 cm · 6,022e23.
l = 7,7e15 cm.
