when evaporation occurs, only the amount of solvent decrease, the amount of solute stays the same. Does the solution become more concentrated or more dilute?

The solution becomes more concentrated

Explanation:

As the solvent evaporates, the solute remains intact. This implies that we have more of the solute than the solvent in the solution. So as the evaporation continues, the resulting solution becomes more concentrated as we now have more of the solute than the solvent.