"Expandable and then return to normal" Image in Storyline 360 Quiz

The simplest way to toggle the image would be to put the larger version into the Selected state. Then you don't need any triggers. When an object has a Normal state and a Selected state, clicking it will toggle between those two states.

Another option is to use the Zoom Picture feature. That automatically increases the size of a picture to fill as much of the player as possible, based on its resolution.