Question : The element with highest first ionisation energy is:
Option 1: Hydrogen
Option 2: Helium
Option 3: Lithium
Option 4: Sodium
Correct Answer: Helium
Solution : The correct option is Helium.
Ionisation energy is the energy required to remove an electron from a neutral atom, forming a positively charged ion. Helium has the highest ionisation energy because it has the smallest atomic size among all the elements and a full electron shell (1s²), making it very stable and resistant to losing its electrons. This results in a high energy requirement to remove an electron from a helium atom.
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