Statement I Helium has the highest first ionisation enthalpy in the periodic table.
Statement II Ionisation enthalpy decreases from top to bottom in a group.

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Statement I is correct but Statement II is incorrect.

Statement I is incorrect but Statement II is correct.

Both Statement I and Statement II are correct but Statement II is not correct explanation of Statement I.

Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.

answer is B.

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Detailed Solution

Helium has the highest first ionisation enthalpy in the periodic table because more force of attraction acts between nuclei and electrons of ls-orbital.
Ionisation enthalpy decreases from top to bottoms in a group due to decrease in effective nuclear charge.

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