Answer:
Mg (atomic number 12)
K (atomic number 19)
Explanation:
The size of an atom is estimated in terms of its atomic radius.
The atomic radius is taken as half of the inter-nuclear distance between two covalently bonded atoms of non-metallic elements or half of the distance (d) between two nuclei in the solid - state of metals.
- Across a period, atomic radii decrease progressively from left to right.
- This is due to the progressive increase in the nuclear charge without increase in the number of electronic shells.
- Down a group, atomic radii increase progressively due to the successive shells of electrons being added which have been compensated for by the increase in nuclear charge.
Cl is further right of Mg in the third period
K is below Na in the first group
