Sucrose is dextrorotatory but after hydrolysis the mixture show laevorotation, this is because of

Sucrose exhibits laevorotation upon hydrolysis due to the specific arrangement of its constituent molecules. When sucrose is hydrolysed, it undergoes a chemical reaction that breaks the glycosidic bond, resulting in the formation of glucose and fructose as individual monosaccharides.
Since the rotation of glucose is opposite in sign to that of fructose, their combined effect leads to the observed laevorotation i.e. (laevorotation of fructose is more than dextrorotation of glucose.)