How many moles of oxygen (O2) are required to produce 40 liters of water (H2O) if there is excess hydrogen (H2)? 2 H2 + O2 → 2 H2O

40.0 moles O2

1.76 moles O2

0.89 moles O2

3.57 moles O2

A4.86 g piece of metal was placed in a graduated cylinder containing 15.5 ml of water. the water level rose to 17.3 ml. what is the density of the metal. i need the steps of how to solve it to so i can use a formula to work out other problems.