- AThe second ionisation energy of $Se$ is greater than that of second ionisation energy of $As$
- BThe first ionisation energy of $C^{2+}$ ion is greater than that of first ionisation energy of $N^{2+}$ ion
- CThe third ionisation energy of, $F$ is greater than that of third ionisation energy of $O$
- ✓Helogens have highest $I.E.$ in respective period