JEE Main 2026 — Classification of Elements and Periodicity in Properties Question with Solution
JEE Main 2026 (06 April Shift 2)
Question
In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively.
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Show full solutionCorrect option: C
Correct answer
Clowest and highest
Step-by-step explanation
In a period, as we move from left to right, the atomic size decreases and the effective nuclear charge increases.
Due to the large atomic size and low effective nuclear charge, the element at the extreme left (alkali metal) has the lowest first ionisation enthalpy in the period.
As we move to the extreme right (excluding noble gases), the elements (halogens) have the smallest atomic size and highest effective nuclear charge in the period. They require only one electron to complete their octet. Thus, they have the highest negative electron gain enthalpy.
Therefore, the first ionisation enthalpy of the extreme left element is the lowest, and the negative electron gain enthalpy of the extreme right element is the highest.
Answer: lowest and highest
Due to the large atomic size and low effective nuclear charge, the element at the extreme left (alkali metal) has the lowest first ionisation enthalpy in the period.
As we move to the extreme right (excluding noble gases), the elements (halogens) have the smallest atomic size and highest effective nuclear charge in the period. They require only one electron to complete their octet. Thus, they have the highest negative electron gain enthalpy.
Therefore, the first ionisation enthalpy of the extreme left element is the lowest, and the negative electron gain enthalpy of the extreme right element is the highest.
Answer: lowest and highest
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This is a previous-year question from JEE Main 2026, covering the Classification of Elements and Periodicity in Properties chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.