Answer:
Potassium (K) has a larger average atomic radius (220 pm) than sodium (Na) does (180 pm). The potassium atom has an extra electron shell compared to the sodium atom, which means its valence electrons are further from the nucleus, giving potassium a larger atomic radius. The ionic radius increases in a particular group on moving from top to bottom due to increase in the principle energy shell though the number or electrons in the valence shell remain the same
