The reaction between metallic Magnesium and steam will be
As per balanced equation:
one mole of Mg will react with two moles of water to give one mole of magnesium hydroxide
Moles of Mg = Mass / atomic mass = 19.4/24 = 0.81
Moles of water = mass / molar mass = 14/18 =0.78
thus here for 0.81 moles of Mg we need twice the moles of water
However we have just 0.78 moles of water it means the limiting reagent is water
The moles of Mg reacted with water = 0.5 X 0.78 = 0.39 moles
moles of Mg left after reaction = 0.81-0.39= 0.42 moles
mass of Mg left (excess reagent) = moles X atomic mass = 0.42 X 24 = 10.08g
The moles of Mg(OH)2 formed = 0.39 moles
mass of Mg(OH)2 formed = moles X molar mass = 0.39 X 58 = 22.62g
I'm guessing it's a completing the answer question
Ok so next time maybe add that it explains the number of covalent bonds in the atom because... (and then explain CaF2 tendencies in following the octet rule, like if it adds to 8 or isn’t completed yet.)
If this isn’t enough I would highly recommend asking your teacher after class even if they don’t like you or are one of THOSE teachers they gotta help you or it’s not fair for them to count you off points.