Answer:
1.95mol
Explanation:
First let us generate the equation for the reaction:
2H2 + O2 —> 2H2O
From the equation,
1mole of O2 reacted to produce 2moles of H2O.
Therefore, Xmol of O2 will react to produce 3.9 mol of H2O i.e
Xmol of O2 = 3.9/2 = 1.95mol