Question

Na pos ion is smaller than Na atom while Cl neg ion is bigger than chlorine atom why

Answer 1

because in sodium positive Ion The outermost one electron has been removed from sodium atom so its size decreases while in chlorine chlorine is an electronegative atom so it gains 1 electron and its size increases

Answer 2

Na(+) - this + means that the atom has donated a electron to any other atom and if any atom donates atom then its size becomes small as the nucleus attracts with more force due to removal of 1 electron.
Cl(-) - this - means that the atom has gained a electron and if any atom gains electron then its size becomes large as the nucleus attracts with less force due to addition of 1 electron..

Hope this helps you.....