2) Which liberates the most energy? A) F(g) + e ➡️ F-(g)
B) N(g) +e- ➡️ N-(g)
C) O(g) +e ➡️ O-(g)
D) C(g) +e ➡️ C-(g)

Explanation:

Electron gain enthalpy is defined as energy released on addition of electron to an isolated gaseous atom.  

The amount of energy released will be maximum when the tendency to attract electrons is maximum. As flourine has atomic number of 9 and has electronic configuration of 2,7. It can readily gain 1 electron to attain stable noble gas configuration and hence liberates maximum energy.