When naming an ionic compound what must always come first the anion or the cation? (Metal or
nonmetal)

Cation / metal

Explanation:

When we named ionic compound we always write cation first. Let's take an example.

Sodium chloride is ionic compound. The electronegativity of chlorine is 3.16 and for sodium is 0.93. There is large difference is present. That's why electron from sodium is transfer to the chlorine. Sodium becomes positive and chlorine becomes negative ion. Both atoms are bonded together electrostatic attraction occur between anion and cations and ionic compound is formed. When we naming it we write " sodium " first which indicate sodium cation ( Na⁺)  while anion which is Cl⁻ is always written at the end. When we naming ionic compound we ended the name of anion with "ide". Sodium indicate metal while chloride ion indicate non metal. it means metal comes first while naming ionic compound.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.