What are the most common types of elements in sandstome

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

Joan writes four numbers on the board in standard form, and then she writes their scientific notation

Which statement best describes the flow of energy in this scenario