21. change in temperature, change in color, or noticeable odor (after reaction has begun)
22. Picture... Wasn't so sure about this since no charge was given, so I suspected it has a charge of 2. If you have more information on this I would be glad to help, and I can't tell what is happening with the calculations given. It would be helpful if you can add spaces or put a line break.
23. An ion is an atom or molecule with an electric charge. It is formed when atoms lose or gain electrons. There are two types of ions: cations (net positive charge) and anion (net negative charge).
24. Picture
25. a) dinitrogen tetrahydride
b) phosphorus triiodide
c) lithium hydroxide
A solution is when a solute dissolves in a solvent. ( I don’t understand the rest of the question)
In solid phase, substances form ordered arrangements called crystalline structures. Whereas in liquid phase molecules are rapidly moving around and disordered.