Number of moles of sn (l) produced when 4.0 moles of h2 (g) is completely consumed

The answer is 2.0 moles.
From their coefficients in the balanced chemical equation below for the reaction of tin dioxide with hydrogen gas to produce tin and water:
     SnO2(s) + 2H2(g) ==>Sn(l) + 2H2O(g)
two moles of hydrogen gas is to produce one mole of tin. We use this mole ratio to compute for the number of moles of tin as:
     moles of Sn = 4.0mol H2 (1mol Sn/2mol H2) = 2.0 mol

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