Question

why the size of sodium is greater than magnesium

Answer 1

Answer:

Because net nuclear charge of nucleus on electron is greater in Magnesium than sodium. So due to effect net charge of nucleus on electron Magnesium shrink

Answer 2

size of sodium is greater than magnesium

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atomic number of Na is 11 and Atomic no of Mg is 12 and there are in horizontal manner with each other ie along the periods

along the periods the atomic size decreases as the atoms are added to the same shell and the nucleus tries to pull the outermost electron more effectively which decreases the size of the element