Question: 62: The correct order of first ionization enthalpy for the given four element is :
(1) \mathrm{C}<\mathrm{N}<\mathrm{F}<\mathrm{O}
(2) \mathrm{C}<\mathrm{N}<\mathrm{O}<\mathrm{F}
(3) \mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}
(4) \mathrm{C}<\mathrm{F}<\mathrm{N}<\mathrm{O}
Answer: Option (3)
Explanation:
First ionization enthalpy is the energy required to remove the most loosely
bound electron from an isolated gaseous atom.
Across a period, first ionization enthalpy generally increases due to increase
in nuclear charge and decrease in atomic size.
Carbon has the lowest ionization enthalpy among the given elements
because it has a relatively larger atomic size and lower effective nuclear charge.
Oxygen has lower ionization enthalpy than nitrogen because nitrogen has a half-filled stable electronic configuration 2p^3,
while oxygen has paired electrons in one of the 2p orbitals,
causing extra electron–electron repulsion.
Fluorine has the highest ionization enthalpy due to its small size and high effective nuclear charge,
which strongly holds the valence electrons.
Therefore, the correct increasing order of first ionization enthalpy is:
\mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}Hence, option (3) is correct.