Question

The first ionisation potential of nitrogen and oxygen atoms are related as follows. (J1989,1M)

• A. The ionisation potential of oxygen is less than the ionsisation potential of nitrogen
  
• B. The ionisation potential of nitrogen is greater than the ionisation potential of oxygen
  
• C. The two ionisation potential values are comparable
  
• D. The difference between the two ionisation potential is too large

Answer 1

Answer: (A), (B), (C)

The two ionisation potential values are comparable


(a) and (b) are infact the same statements and both are correct. N has slightly greater ionisation energy than oxygen which is against periodic trend. This exception is due to completely half -filled $\left(2p^3\right)$ orbital in nitrogen that makes ionisation slightly difficult than oxygen.
(c) Also correct: Although N has greater first ionisation potential than oxygen, two values of ionisation potentials are comparable since they are adjacent in a period. i.e. electrons are removed from same orbit during ionisation.
(d) Incorrect -opposite to (c). of the bonded atoms which in turn has periodic trend in long form of periodic table.