Chemistry?

1. When one mole of oxide of metal M, M3O4, is reduced by excess hydrogen gas, what is the maximum mass that may be reduced?
A. 16g
B. 18g
c. 48g
D. 64g

2. MH2(g) + 2H2O(l)→M(OH)2(s) + 2H2(g)
0.42g of dry hydrogen gas was liberated at STP.Calculate the relative atomic mass of M.
Answer given is 40.
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