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Periodic Table, Periodic Properties and Variations of Properties — Chemistry STD 10 — Question

ICSE BoardEnglish MediumSTD 10ChemistryPeriodic Table, Periodic Properties and Variations of Properties1 Mark
MCQ
Which of the following pairs does the second element have a higher 1st ionisation enthalpy than the 1st element?
  • A
    First element-Mg Second element- Al
  • B
    First element-N Second element- O
  • C
    First element-Ne Second element- Na
  • ✓
    First element-K Second element- Na
✓

Answer

Correct option: D.
First element-K Second element- Na
(d) First element-K Second element- Na
Explanation : The miniumum energy required to remove one electron from the valence shell of an isolated gaseous atom is called ionisation enthalpy. As we move left to right in a period, ionisation enthalpy increases, due to the increase in nuclear charge while as we move top to bottom in a group ionisation enthalpy decreases due to increase in number of shells, which decreases the effective nuclear charge acting on the valence electrons.
In option (d), Sodium is present in the second period while Potassium is in the third period of the same group. Thus, sodium have a higher $1^{\text {st }}$ ionisation enthalpy than the $1^{\text {st }}$ element that is Potassium.

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