What does a refractive index from medium 1 to medium 2 mean? isn't one of the medium must be vacuum?

Refractive index is the measure of bending of a ray of light when passing from one medium into another. It is not necessary that one medium must be vaccum.

For example, the image below shows refraction, where first medium is air and second medium is water.

the best answer for these questions would be:

1.            c. is smaller

2.            d) concrete operational

3.            b) interaction with the environment – the children interact with their environment can them learn more.

4.            a) parents who reason openly with children can limit a child’s cognitive ability.

the right answer is 0.3 meters per second