The density of a substance is defined as its

Density is the mass per unit volume

Density is actually is the ratio of the mass of an object to its volume. It is used to compare the different objects on the basis of their weight. You can say that more the weight of an object more will be its density. For example, the density has the role in floating the ships on the water. When we insert the wooden piece inside water it pops up to the surface. The weight of the wood piece is more than the water and volume is greater which affects its density. When the object gets smaller the size on pressing, the density of the object increase.

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.

the answer is b

explanation: