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Periodic Table and Periodicity question

2021 · 31 Aug · Shift 1 · Q9
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Periodic Table and Periodicity question

2021 · 31 Aug · Shift 1 · Q9

JEE MainChemistryPeriodic Table and PeriodicityMCQ+4 / −1
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Metallic character decreases and non-metallic character increases on moving from left to right in a period. Reason (R) : It is due to increase in ionisation enthalpy and decrease in electron gain enthalpy, when one moves from left to right in a period. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    (A) is false but (R) is true.
  2. B
    (A) is true but (R) is false
  3. C
    Both (A) and (R) are correct and (R) is the correct explanation of (A)
  4. D
    Both (A) and (R) are correct but (R) is not the correct explanation of (A)
View written solutionFree

Correct answer: B

  1. Check the Assertion (A):
    Across a period from left to right:

    • effective nuclear charge increases,
    • atomic size decreases,
    • atoms lose electrons less easily and gain electrons more readily.

    Hence, metallic character decreases and non-metallic character increases from left to right in a period.
    So, Assertion (A) is true.

  2. Check the Reason (R):
    The reason says this happens due to:

    • increase in ionisation enthalpy and
    • decrease in electron gain enthalpy on moving left to right in a period.

    Let us examine both parts:

    • Ionisation enthalpy generally increases across a period — this is correct.
    • But electron gain enthalpy does not decrease; rather, it generally becomes more negative across a period (i.e. electron gain tendency increases), with some exceptions.

    Therefore, the statement "decrease in electron gain enthalpy" is incorrect in the intended periodic-trend sense. The non-metallic character increases because atoms have greater tendency to accept electrons, not less.

    So, Reason (R) is false.

  3. Conclusion:

    • Assertion (A): True
    • Reason (R): False

    Therefore, the correct option is: B: (A) is true but (R) is false\boxed{\text{B: (A) is true but (R) is false}}B: (A) is true but (R) is false​

  4. Comparison with stored answer:
    Stored correct answer is B, which matches the derived answer.

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