Answer : The correct statement is, the third beaker does not dissolve as fast as one and two.
Explanation :
According to the question, we know that the dissolving process is faster in case of heating as compared to the stirring. And the dissolving process also depends on the how much amount of heat are provided to the substance or the how much faster will you stirring mixture.
The second beaker dissolves faster than the other two, this statement is true but we do not know the how much heat are given to the beaker.
From the given statements we conclude that the correct statement is, the third beaker does not dissolve as fast as first and second beakers because in the third beaker there is no heat or mechanical energy are provided for mixing of the substance.
Hence, the correct statement is, the third beaker does not dissolve as fast as one and two.