Good: There is an educational element, although the choice of font made it sometimes difficult to read.
Room for improvement: The audio is very on the nose and works as a distraction most of the time. I would have loved if combining the elements had some greater impact/give the player different abilities, just something to give more value to the changed state other than some different letter.
All in all the game feels very rough still, but it does fulfill the purpose it was designed for, which (i think) is giving a better understanding of the elements.
I'm sure your future projects will only become better from this point on, keep going!
Edit: Tip for future submissions with Godot, pack both the .exe file and the pck file into a .zip or .rar file, that way you can upload a single file that people can unzip, instead of uploading your project in two pieces :)