Answer: Option (A) is the correct answer.
Explanation:
When solute dissolved faster in one beaker then it means the rate of dissolution is faster as no other substance except the solute is present in the solution.
Whereas, in another beaker solute dissolved slowly therefore, rate of dissolution of solute is slow as it might be possible that some other substances including the solute are present in the solvent.
As a result, rate of dissolution has decreased into the water (solvent).
Since it is given that temperature was same in both the beakers. Thus, there is possibility that one of the beaker already had some solute.
Hence, we can conclude that the beaker that dissolved the solute slower already has some solute in it.