Which group 2a element has the largest ionic radius? magnesium calcium barium radium

Radium has the largest ionic radius because when you go down a group the ionic radius gets bigger as you go down and out of these elements Radium is the lowest

This is what i found on google “according to the collision theory, the following criteria must be met in order for a chemical reaction to occur: molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break. molecules must collide with the proper orientation.” i hope this information you.