Number that indicates how many electrons an atom must gain lose or share to become stable

Ionic charge

Explanation:

Group1- 1+

Group2- 2+

Group13- 3+

Group15- 3-

Group16- 2-

Group17- 1-

That's thier ionic charge

the answer is either b or c

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.