If the first ionisation enthalpy of $\mathrm{Li}, \mathrm{Be}$ and C respectively are $520,899,1086…
If the first ionisation enthalpy of $\mathrm{Li}, \mathrm{Be}$ and C respectively are $520,899,1086 \mathrm{~kJ} \mathrm{~mol}^{-1}$, the first ionisation enthalpy (in $\mathrm{kJ} \mathrm{mol}^{-1}$ ) of B will be
487
950
801
1402
Solution
First ionisation enthalpy of $\mathrm{Li}, \mathrm{Be}$ and C respectively are $520,899,1086 \mathrm{~kJ} \mathrm{~mol}^{-1}$.
The ionisation energy depend on the
(i) Size of the atom
(ii) effective nuclear charge
(iii) Screening effect
(iv) Penetration effect
(v) Electronic configuration
$\begin{aligned}
& \mathrm{Li}-1 \mathrm{~s}^2 2 \mathrm{~s}^1 \\
& \mathrm{Be}-1 \mathrm{~s}^2 2 \mathrm{~s}^2 \\
& \mathrm{~B}-1 \mathrm{~s}^2 2 \mathrm{~s}^2 2 \mathrm{p}^1 \\
& \mathrm{C}-1 \mathrm{~s}^2 2 \mathrm{~s}^2 2 \mathrm{p}^2
\end{aligned}$
(i) Left to right in the periodic table ionisation enthalpy increase.
(ii) Beryllium have full filled orbital so its ionisation energy is more than boron.
So, order will be.
$\begin{aligned}
& \mathrm{C}\gt\mathrm{Be}\gt\mathrm{B}\gt\mathrm{Li} \\
& 1086\gt899\gt{----}\gt520
\end{aligned}$
So, the value of Boron in between 899 to 520 .
$\therefore$ Correct option will be (c). which is 801 value for Boron.