Formula for magnetic moment =√n(n+2)=μ,
Where n is no. of unpaired electrons
∵μ=0,
⇒√n(n+2)=0
⇒n(n+2)=0.
Product of two integer can only be zero; only if one of them is zero.
So, n=0
∵ For diamagnetic substance; no. of unpaired electrons is zero.
So, if magnetic moment of atoms of a substance is zero; the substance is diamagnetic.