Which of these statements is correct about wood and common salt?

a.) both wood and common salt are minerals because they are natural, solid materials.

b.) both wood and common salt are not minerals because they are not formed under the ground.

c.) common salt is a mineral because it has a definite crystal structure but wood is not a mineral because it is organic.

d.) common salt is not a mineral because it is not formed under the ground but wood is a mineral because it has a definite composition.

Option (C) is the correct answer.

Explanation:

Minerals are inorganic substances which have certain characteristic shape or structure along with homogeneous chemical composition.

It is not necessary that a mineral should be formed under the ground.

Substances which have carbon atoms in their structure are called organic compounds.  The structure of wood has carbon atoms attached thus, wood is an organic compound.

Therefore, we can conclude that common salt is a mineral because it has a definite crystal structure but wood is not a mineral because it is organic.

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.