Question

give one example each of a situation in which sieving an winnowing can be used for bringing about the required separation​

Answer 1

yes but not that level that it has no impurities

Answer 2

sieving allows the fine flour particles to pass through the holes of the sieve while the bigger particles is impurities remain on the sieve example in flour mill impurities like husk and stones are removed from the wheat before grinding it.