If you have to write the chemical formula of a simple, binary ionic compound given the name of the compound, you follow a set of three steps. Let's go through them using magnesium chloride as an example. Write the symbols for the cation and the anion: Mg and Cl. Determine the charge on the cation and anion.
Answer:
I believe the answer is C. Stopping an object from moving
Answer: 26.7 moles
Explanation: 
As can be seen from the balanced chemical equation 2 moles of hydrogen combine with 1 mole of oxygen to give two moles of water.
1 mole of oxygen give = 2 moles of water.
Thus 13.35 moles of oxygen give=
of water.