Answer:
1.6mole of H2O 
Step-by-step explanation:
First let us generate a balanced equation for the reaction. This is illustrated below:
2H2 + O2 —> 2H2O
Molar Mass of O2 = 2 x 16 = 32g/mol. 
Mass of O2 = 25.6g
Number of mole of O2 = Mass /Molar Mass 
Number of mole of O2 = 25.6/32
Number of mole O2 = 0.8mol 
From the equation, 
1mole of O2 produced 2moles H2O. 
Therefore, 0.8mol of O2 will produce = 0.8 x 2 = 1.6mole of H2O