- A$C > N > O > F$
- B$O > N > F > C$
- ✓$O > F > N > C$
- D$F > O > N > C$
$\mathrm{N}(7) \quad 1 \mathrm{s}^{2} 2 \mathrm{s}^{2} 2 \mathrm{p}_{\mathrm{x}}^{1} 2 \mathrm{p}_{\mathrm{y}}^{\mathrm{i}} 2 \mathrm{p}_{\mathrm{z}}^{1}$
$\mathrm{O}(\mathrm{8}) \quad 1 \mathrm{s}^{2} 2 \mathrm{s}^{2} 2 \mathrm{p}_{\mathrm{x}}^{2} 2 \mathrm{p}_{\mathrm{y}}^{1} 2 \mathrm{p}_{\mathrm{z}}^{1}$
$\mathrm{F}(9) \quad 1 \mathrm{s}^{2} 2 \mathrm{s}^{2} 2 \mathrm{p}_{\mathrm{x}}^{2} 2 \mathrm{p}_{\mathrm{y}}^{2} 2 \mathrm{p}_{\mathrm{z}}^{1}$
$O$ has highest $2^{\text {nd }}$ ionisation potential i.e ionisation energy because after losing one electron, it acquires noble gas configuration.
$\mathrm{F}$ is smaller than $\mathrm{N}$, therefore, it has higher second ionisation potential. $C$ has least due to bigger size.
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$CaCO _{3}( s ) \rightarrow CaO ( s )+ CO _{2}( g )$ the values of $\Delta H ^{\circ}$ and $\Delta S^{\circ}$ are $+179.1 kJ mol ^{-1}$ and $160.2\,J / K$ respectively at $298 \,K$ and $1 \,bar$. Assuming that $\Delta H ^{\circ}$ and $\Delta S ^{\circ}$ do not change with temperature, temperature above which conversion of lime-stone to lime will be spontaneous is ........... $K$

$3 s^{2}$; $3 s^{2} 3 p^{1}$; $3 s ^{2} 3 p ^{3}$; $3 s^{2} 3 p^{4}$
The correct order of first ionization enthalpy for them is.
Reason : The only property that determines its aromatic behaviour is its planar structure.
