Okay kiddo, so have you ever seen a balloon filled with air? When you let the air out of the balloon, it spreads out and fills up the space around it, right? Now imagine that the space around the air is filled with water.
When certain substances are dissolved in water, they release electrons. These electrons are kind of like invisible balls that are negatively charged. But when they're in water, they don't just bounce around like a ball would. Instead, they get surrounded by water molecules, kind of like how the air in the balloon is surrounded by water.
This group of water molecules and electrons together is called a solvated electron. The water molecules keep the electrons from escaping or colliding with other things, which is important because when electrons bounce around too much they can become really reactive and cause damage.
Scientists study solvated electrons because they can help us understand how different substances interact with each other and with water. Plus, they're kind of neat to look at under a microscope!