The answer is A.) 2.5 mol H2O2. It is through decomposition that the old elements are usually broken down into new pieces that can still be useful for the environment. It should also be a balanced equation where no elements are removed nor added. 2 moles of H2O2 will yield to 1 mole of O2.
So following this simple ratio, 4 moles of H2O2 will result in 2 moles of O2. For 1 mole of H2O2, it will yield to 0.5 moles of O2. Adding those up, 5 moles of H2O2 will yield to 2.5 moles of O2. You can write it in its formula: 5 moles H2O2 x (1-mole O2/2 moles H2O2) = 2.5 moles O2.
Given: 5 mol H2O2
Unknown: ? mol O2
5 mol H2O2 x (1 mol O2/2 mol H2O2) = 2.5 mol = 3 mol O2
Although 2.5 mol O2 is technically correct, your answer must include the correct number of significant figures (which in this instance is 1). The answer is rounded to 3.