Step 1: Understanding the comparison.
Hydrogen shows similarities with both alkali metals and halogens due to its unique position in the periodic table. Some of its properties resemble halogens.
Step 2: Ionisation enthalpy comparison.
Halogens possess high ionisation enthalpy values, and hydrogen also has a relatively high ionisation enthalpy compared to alkali metals. This similarity is one of the reasons hydrogen is sometimes compared with halogens.
Step 3: Analysis of options. (A) Ionisation enthalpy: Correct — hydrogen and halogens both have high ionisation enthalpy values. (B) Formation of unipositive ion: Incorrect — this is a property similar to alkali metals. (C) Electronic configuration: Incorrect — hydrogen has \(1s^1\), while halogens have \(ns^2 np^5\). (D) Electron gain enthalpy: Incorrect — halogens have very high electron gain enthalpy, much higher than hydrogen.
Step 4: Conclusion.
Ionisation enthalpy is the property of hydrogen that is similar to the halogen family.