In 4 2 he 24he , what does the number 4 indicate?

The number 4 indicates the mass number of the element.

Explanation:

The mass is defined as the number of nucleons in the nucleus of the element.

Let an element is

Here Z is the number of protons in the nucleus

A be the number of nucleons in the nucleus

The number of nucleons is the sum of number of protons and the number of neutrons.

So, the number of protons in the nucleus are Z, number of neutrons are A - Z in the nucleus.

Thus, 4 indicates the sum of number of protons and the neutrons.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.