Lactose being a disaccharide gives two molecules of monosaccharides i.e. one molecule each of D-(+) glucose and D-(+)-galactose.
\(\underset{\text { Lactose }}{\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}}+\mathrm{H}_2 \mathrm{O} \underset{\text { Lactose }}{\stackrel{\mathrm{H}_3 \mathrm{O}^{+}}{\longrightarrow}} \underset{\text { D-(+)-Glucose }}{\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6}+\underset{\mathrm{D}-(+)-\mathrm{Galactose}}{\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6}\)