Potassium permanganate as a compound formula

KMnO4

Explanation: Potassium K has a charge of +1 since it is a cation and in group 1. Permanganate is a polyatomic ion with a chemical formula of MnO4 - it is an anion with a -1 charge.

Do the criss cross rule on both charges and the result is KMnO4. The charge will cancel out since they are equal values.

The number of phosphorus atoms : 2.408 x 10²⁴

The mole is the number of particles(molecules, atoms, ions) contained in a substance  

1 mol = 6.02.10²³ particles

Can be formulated

N=n x No

N = number of particles

n = mol

No = Avogadro's = 6.02.10²³

moles of Mg₃(PO₄)₂ = 2

moles of phosphorous(P) atoms in Mg₃(PO₄)₂ ⇒ mol ratio of elements in the compound(for P=2)

The number of atoms of  phosphorous(P) :