Question

why do we need to seprate substanes?

Answer 1

we need to separate substances
it is very important so that all the substances can be used individually.

few weeks impurities will me mixed with food items like stones husk etc so as to remove the impurities we need to separate the substances.

Answer 2

In a mixture there are two or more substances mixed. Separation of these substances are important so that all the substances can be used individually. There are different methods which is used to separate substances. For example, handpicking, threshing, filtration, sedimentation, winnowing, etc.