Equation to calculate percentage uncertanty

Can someone me with these questions plz.

How many liters of hydrogen gas will be produced at stp from the reaction of 7.179×10^23 atoms of magnesium with 54.219g of phosphoric acid (h3po4) the equation is 3mg + 2h3(> mg(po4)2+3h2

What type of electromagnetic radiation has a shorter wavelength than blue light