Natural wool is attacked by moth, whereas acrylic wool is not. Explain.

That would be because the natural wool fiber is produced by a living thing, a sheep.  So the wool is the remains of a living cells, which could be used as a food source by insects, such as moths.  Acrylic wool, on the other hand, is produced from synthetic sources, such as plastics or nitriles.  Acrylic wool is basically a form of plastic, much the same as plastic bottles or milk jugs.  A simple test...

That would be because the natural wool fiber is produced by a living thing, a sheep.  So the wool is the remains of a living cells, which could be used as a food source by insects, such as moths.  Acrylic wool, on the other hand, is produced from synthetic sources, such as plastics or nitriles.  Acrylic wool is basically a form of plastic, much the same as plastic bottles or milk jugs.  A simple test would be to take a length of wool yarn and an acrylic yarn and set them on fire.  The wool yarn will burn easily, leaving a fragile ash behind.  The acrylic yarn will have a blackish smoke and smell oily.  Another test would be to cut two pieces of yarn and try to twist them together.  The wool yarn will twist together easily, forming one piece between the two.  The acrylic yarn will not meld together easily, will tend to come apart.