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KCET2010ChemistryThermodynamics (C)

Generally, the first ionization energy increases along a period. But there are some exceptions. One which is not an exception is

Options

  1. AN and O
  2. BNa and Mg
  3. CMg and Al
  4. DBe and B

Correct answer

B. Na and Mg

Step-by-step solution

Na belongs to IA group and Mg belongs to IIA group. On moving form left to right in a period, first ionization energy increases, thus, IE of Mg is greater than the IE of Na. IE order Mg > Na

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