Give reasons:
(a) Sand and saw dust cannot be separated by hand picking.
(b) Magnet is used to separate a mixture of iron and sulphur.

(a) In handpicking method, the components of a mixture should be large enough in size to be recognized and picked out by hand but sand and saw dust particles are very small in size so they can’t be picked by hand.
(b) Mixtures of iron and sulphur can be separated by moving a magnet over them. Iron gets attached to the magnet and hence gets separated.