The electron affinity values of Be, Mg are zero and those of N (0.02 eV) and P(0.80eV) are very low

Explanation

The electron affinities of Be . Mg and noble gases are almost zero because both `(Z=4:1s^(2)2s^(2))and "Mg" (Z=12,1s^(2)2s^(2)2p^(6)3s^(2))` are having s orbital fully filled in their valence shell . Fully filled orbitals are most stable due to symmetry. Therefore , these elements would be having least tendency to accept electron . Hence. Be and Mg would be having zero electron affinity Whereas
`N(Z=7,1s^(2)2s^(2)2px^(1)2py^(1)2pz^(1))and P(Z=15)1s^(2)2s^(2)2p^(6)3s^(2)3p^(3)` is having half filled 2p - subshell . Half filled sub shells are most stable due to symmetry (Hund 's rule). Thus , nitrogen and phosphorous are having least tendency to accept electron Hence ,have low electron affinity.