To calculate the frequency of an electromagnetic wave, you need to know the speed of the wave which you already know as 186000 miles per second and its
a. refraction intensanator
b. amplitude divisor coefficient
c. intensity lumenous
d. wavelength

D. Wavelength

Explanation:

Frequency is the number of waves that pass through a given point in a given amount of time. You've been given the speed and amount of time, all that's remaining is the wavelength.

Blue vitriol is crystal copper sulphate

Explanation:

The black oxide is the higher oxide of Copper i.e Cu. It is also called as tenorite. It is solid black in color. It is formed by heating copper with air.

Blue vitriol is the crystalline form of copper sulphate. It is also known as copper (II) sulphate.

When heating, the blue vitriol undergoes various steps of changes to the black oxide of copper.

The chemical reaction is --