My question is this : what is the property of transparent material that is used for lens?. I think that it allows the light to pass through ( absorption property) and does not bend the light ( refraction property). But my multiple choice homework has one answer " absorption" and the other " refraction" . So based on my understanding, what is wrong?
The allowing of light to pass through is actually the opposite of absorption: absorption is where the energy of the light beam is permanently transferred to the medium and converted e.g. to heat. Ideally, a lens would not absorb light at all, and would interact elastically with it. In practice, one cannot avoid a tiny amount of absorption, but this is a non-ideal effect: "refraction", being the change in propagation speed of the disturbance as a function of position, is the key property that enables a lens to work. You can indeed show that the speed change - varying refractive index with position - implies Snell's law and is what bends light: I show this from Maxwell's equations in this answer here and here