Answer is: number of atoms in a copper rod is 2.89·10²⁴.
r(Cu) = 1.05 cm; radius of copper rod.
l(Cu) = 9.85 cm; lenght of copper rod.
V(Cu) = r²(Cu) · π· l(Cu).
V(Cu) = (1.05 cm)² · 3.14 · 9.85 cm.
V(Cu) = 34.1 cm³, volume of copper rod.
m(Cu) = d(Cu) · V(Cu).
m(Cu) = 8.96 g/cm³ · 34.1 cm³.
m(Cu) = 305.53 g; mass of copper.
n(Cu) = m(Cu) ÷ M(Cu).
n(Cu) = 305.53 g ÷ 63.55 g/mol.
n(Cu) = 4.81 mol; amount of substance.
N(Cu) = n(Cu) · Na (Avogadro constant).
N(Cu) = 4.81 mol · 6.022·10²³ 1/mol.
N(Cu) = 2.89·10²⁴.
