Question:
In a period, ionization energy of left most element is _ _ _ _ _ _ _ _ and \(|\Delta H_{eg}|\) value of right most element is _ _ _ _ _ _ _ _ . [Except noble gases]
In a period, ionization energy of left most element is _ _ _ _ _ _ _ _ and \(|\Delta H_{eg}|\) value of right most element is _ _ _ _ _ _ _ _ . [Except noble gases]
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Across a period, ionization energy generally increases and electron gain enthalpy becomes more negative. So, alkali metals have the lowest ionization energy, while halogens have the highest \(|\Delta H_{eg}|\) value.
Updated On: Apr 7, 2026
- lowest, lowest
- lowest, highest
- highest, highest
- highest, lowest
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The Correct Option is B
Solution and Explanation
Step 1: Understanding ionization energy across a period.
In a period, atomic size generally decreases from left to right because nuclear charge increases while electrons are added to the same shell.
Due to this stronger attraction between nucleus and valence electrons, ionization energy generally increases from left to right.
Therefore, the left most element of a period has the lowest ionization energy.
Step 2: Understanding electron gain enthalpy across a period.
Electron gain enthalpy generally becomes more negative from left to right across a period because the tendency to accept an electron increases.
Since the question asks for \(|\Delta H_{eg}|\), we consider the magnitude of electron gain enthalpy.
The right most element in a period, excluding noble gases, is generally a halogen.
Halogens have the highest value of \(|\Delta H_{eg}|\) because they most readily gain an electron.
Step 3: Checking the options.
(A) lowest, lowest is incorrect because the right most element does not have the lowest \(|\Delta H_{eg}|\).
(B) lowest, highest is correct because the left most element has lowest ionization energy and the right most element has highest \(|\Delta H_{eg}|\).
(C) highest, highest is incorrect because the left most element does not have highest ionization energy.
(D) highest, lowest is incorrect for both parts.
Step 4: Conclusion.
Hence, in a period, the ionization energy of the left most element is lowest and the \(|\Delta H_{eg}|\) value of the right most element is highest.
Final Answer: (B) lowest, highest
In a period, atomic size generally decreases from left to right because nuclear charge increases while electrons are added to the same shell.
Due to this stronger attraction between nucleus and valence electrons, ionization energy generally increases from left to right.
Therefore, the left most element of a period has the lowest ionization energy.
Step 2: Understanding electron gain enthalpy across a period.
Electron gain enthalpy generally becomes more negative from left to right across a period because the tendency to accept an electron increases.
Since the question asks for \(|\Delta H_{eg}|\), we consider the magnitude of electron gain enthalpy.
The right most element in a period, excluding noble gases, is generally a halogen.
Halogens have the highest value of \(|\Delta H_{eg}|\) because they most readily gain an electron.
Step 3: Checking the options.
(A) lowest, lowest is incorrect because the right most element does not have the lowest \(|\Delta H_{eg}|\).
(B) lowest, highest is correct because the left most element has lowest ionization energy and the right most element has highest \(|\Delta H_{eg}|\).
(C) highest, highest is incorrect because the left most element does not have highest ionization energy.
(D) highest, lowest is incorrect for both parts.
Step 4: Conclusion.
Hence, in a period, the ionization energy of the left most element is lowest and the \(|\Delta H_{eg}|\) value of the right most element is highest.
Final Answer: (B) lowest, highest
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