Okay, so you know how Earth and Mars are both planets right? Well, Mars is a very dry and dusty planet, but scientists have discovered that there are some areas on Mars where there are special minerals called chlorides.
Now, these chlorides are just like little tiny grains of sand, but they are special because they contain a chemical called chlorine. Chlorine is a stinky gas that we use to clean swimming pools, but on Mars, it has been trapped inside these tiny grains of sand.
Scientists are really interested in these chloride deposits on Mars because they can tell us a lot about the history of the planet. You see, these deposits are formed when water evaporates from the ground, leaving behind the chlorides. So, the presence of these deposits means that Mars must have had water at some point in its history!
By studying the chlorides, scientists can learn more about the conditions that existed on Mars long ago. They can also look for signs of life on the planet. That's because here on Earth, many living things also use chlorine in their bodies.
So, in summary, chloride-bearing deposits on Mars are tiny grains of sand that contain a chemical called chlorine, which could tell us about the history of the planet and even the possibility of life on Mars.