Which of the following is the correct order of ionisation energy?

$\text{ i) }{\mathrm{Be}}^{+}>\mathrm{Be}$

$\text{ ii) }\mathrm{Be}>{\mathrm{Be}}^{+}$

$\text{ iii) }\mathrm{C}>\mathrm{Be}$

$\text{ iv) }\mathrm{B}>\mathrm{Be}$

Be has a completely filled stable valence shell configuration i.e. 2s² while in Be⁺ because of positive charge, the removal of electron requires much higher energy. So, the ionisation energy of Be⁺ is greater than Be
Across the period, atomic size decreases and nuclear charge increases and thus valence shell electron(s) are tightly held by the nucleus. So, the ionisation energy of C is greater than Be.

$\text{ I.E }\Rightarrow {\text{ I.E }}_1<{\text{ I.E }}_2$

$\text{ I. }{E}_1\Rightarrow \mathrm{Be}>\mathrm{B}<\mathrm{C}$

$(\mathrm{B}<\mathrm{Be}<\mathrm{C})$