Explanation:
Hi for this one u just need to remember and use the equation.
[tex]moles = \frac{mass}{mr} [/tex]
then u find mr of potassium which is 39.1.
then u do
[tex] \frac{20}{39.1} [/tex]
you get the answer as 0.5115 write ur answer to 3 significant figures which will be 0.512 moles .
hope this helps :)
