20 g O2 x 1 mol O2/32 g O = 0.625 mol O2
<span>Lithium atoms have one valence electron, where as oxygen atoms have six. Lithium atoms tend to give up their single valence electrons, and oxygen tends to gain two valence electrons from other atoms, like lithium. They do this so they will have filled valence shells. hope this answers your question :)</span>
If one starts with 0.020 g of Mg, 0.0008 moles of H2 would be made if the reaction is complete.
Going by the balanced equation of reaction in the image, 1 mole of Mg will produce 1 mole of H2 in a complete reaction.
If 0.020 g of Mg is started with:
mole of Mg = mass/molar mass
= 0.020/24.3
= 0.0008 moles
Since the mole of Mg to H2 is 1:1, thus, 0.0008 moles of H2 will also be made from the reaction.
More on stoichiometry can be found here: brainly.com/question/9743981