Amolecule has two atoms that are bonded to the central atom and one lone pair of electrons around this central atom. what is the shape of the molecule?
bent
linear
trigonal planar
trigonal pyramidal

Bent, the lone pair on the central atom push away the other atoms and the most stable configuration of the lone pair and two atoms is trogonal planar. But since you cannot see the lone pair, the shape of the three atoms is bent.

The teacher is mostly talking about the distillation of a mixture