Question

A chemist needs 0.0700 mol of potassium for a reaction. What mass of potassium should the chemist use?

Answer 1

1 mol of potassium ------ 39 u
so, 0.0700 mol of K ----- (39*0.0700) = 2.73 u (i don't know if they are asking for grams. if they ask it directly, you might put this answer. If not, convert this amu mass to grams)

Answer 2

Potassium is not available in its elemental form like sodium. I am sure it is available only as its inorganic salts say potassium chloride or iodide or bromide etc. For sake of theory the answer by maddyx holds good but if u re looking for an answer that u can right away use in a lab then u shd also take the contribution of potassium in say KCl .