Which solution is the most concentrated

The most concentrated solution is the one with the highest molarity. Molarity is calculated by taking the moles of solute/ liters of solution. The already gave you the molarity, so you do not need to calculate it. The most concentrated solution is the 0.25 M KCl.

Hope this helps!

- "the choice that is not an indicator of a chemical change is "state of matter changes". more common than not, chemical reactions produce energy in the form of light or heat. along with energy, they also produce a new substance called the product that could be in any state of matter (solid, gas, or liquid)."

that's what i got you can count the number of atoms