Which from following elements has highest value of ionization enthalpy \(\left(\Delta_1 \mathrm{H}_1\right)\) ?

The ionization enthalpy (I.E.) is highest for the inert gases. Therefore I.E of Ar and He will be higher than the halogens Cl and I .
Down the group, I.E decreases due to increase in the atomic size.
Therefore, ionization enthalpy of \(\mathrm{He}\gt\mathrm{Ar}\). varies as: \(\mathrm{I} \lt \mathrm{Cl}\) and \(\mathrm{Ar} \lt \mathrm{He}\).
Across a period, I.E increases with increase in atomic number.
Therefore, I.E of Cl and Ar is in the order: \(\mathrm{Cl} \lt \mathrm{Ar}\).
Hence, the correct increasing order of ionization enthalpy for the given elements is:
\(\mathrm{I} \lt \mathrm{Cl} \lt \mathrm{Ar} \lt \mathrm{He}\)
He has the highest I.E.