Take three bowls and mark as A, B, C. Pour lukewarm milk in bowl A, hot milk in bowl B, cold milk in bowl C. Add one tea spoon of curd or butter milk in three bowls and stir them slightly. Cover the bowls with lids. Keep the bowls undisturbed for five to six hours. In which bowl milk turned into curd? Give your reasons.

The milk will be turned into curd in bowl A and not in other bowls.

Explanation: Lactobacillus is the bacteria required for the formation of curd and it requires an appropriate temperature for its growth. Lukewarm milk not being very much cool and hot provides that appropriate temperature and hence lukewarm milk get converted into milk.

But bowl B and C contains hot and cold milk which do not provide appropriate temperature for the growth of bacteria due to which bacteria doesn’t grow in them and they are not converted into curd.