Question

helium is diamagnetic in nature justify

Answer 1

since the two electrons are in 1s state ,they must have opposite spin according to the Pauli exclusion principle for helium 4

Answer 2

Diamagnetic substances contain no unpaired electrons in their atoms
Example : Helium

Explantion:

Helium Symbol - He with atomic number -2

Electronic configuration-1s²

here s orbital contains 2 electrons which is the maximum capacity that an s orbital can hold.and both the electrons in s orbital are paired.

Conclusion:
As helium has no unpaired electrons  --- It is diamagnetic in nature.