Answer: 
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.
Carbon atom with iron and helium
Answer: 1.284M NH3
Explanation: (12.23 grams)/(17.0 gramms/mole) = 0.7191 moles
Dissolved in 560.0 ml (=0.5600L)
(0.7191 moles)/(0.560L) = 1.284M (4 sig figs)