If you were to react 4.3 miles of magnesium phosphide how many moles of potassium would you need?

25.8

Explanation:

Let's write the reaction between magnesium-phosphide and potassium:

Mg3P2 + K = Mg + K3P

And now let's balance this equation:

Mg3P2+6K=3Mg+2K3P

We see that the ratio of magnesium-phosphide and potassium is 1:6, which means that for every mole of magnesium-phosphide there need to be 6 moles of potassium.

Since we have 4.3 moles of Mg3P2, there need to be 6 • 4.3 = 25.8 moles of potassium.