Consider the reaction.

which statement is true at stp? (the atomic mass of mg is 24.31 u.)
3.0 g of mg produce 3.0 l of h2 gas.
3.0 g of mg produce 22.4 l of h2 gas.
24.31 g of mg produce (3 22.4) l of h2 gas.
(3 24.31) g of mg produce (3 22.4) l of h2 gas.

Answer is: (3 24.31) g of Mg produce (3 22.4) L of H2 gas.

Balanced chemical reaction:

3Mg(s) + 2H₃PO₄(aq) → Mg₃(PO₄)₂(s) + 3H₂(g).

From chemical reaction: n(Mg) : n(H₂) = 3 : 3 (1 : 1).

n(Mg) = n(H₂).

m(Mg) = 24.31 g; mass of magnesium.

n(Mg) = m(Mg) ÷ M(Mg).

n(Mg) = 24.31 g ÷ 24.31 g/mol.

n(Mg) = 1 mol; amount of the magnesium.

V(H₂) = n(H₂) · Vm.

V(H₂) = 1 mol · 22.4 L/mol.

V(H₂) = 22.4 L; volume of the hydrogen gas.

So, 3·24.31 g of magnesium (3 mol) produce 3·22.4 liters of hydrogen.

nuclear fission produces elements that are heavier than helium.

the elements that are used in nuclear fission and their products are much heavier than helium.