Is Matter Around Us Pure? — Science STD 9 — Question

The mixture of mustard oil and water is put in separating funnel and allowed to stand for some time. The mixture separates into two layers according to the densities of water and mustard oil. Water is heavier than mustard oil. So, water forms lower layer while mustard oil forms upper layer. On opening the stop clock of separating funnel, the lower layer of water comes out first and collected in beaker leaving behind mustard oil.