Mg3(PO4)2 - the molar mass would be 262g/mol, which is 100%
Atomic mass of Mg is 24, since we have 3Mg we multiply by 3 and get a mass of 72
262 : 100% = 72 : x%
x = 72*100 / 262
x = 27.5%
And do that for every element — get the molar mass of P and multiply by 2, use a ratio, and get the molar mass of O and multiply by 8 and use ratios :)
The elements of the "Noble" gases group is nonreactive. The reason for this is that noble gases are always or most of the time at room temperature.<span />
Neither of them are used in magnets they don’t attract metal
Answer: 9.9 grams
Explanation:
To calculate the moles, we use the equation:

a) moles of 

b) moles of 


According to stoichiometry :
1 mole of
combine with 1 mole of
Thus 0.33 mole of
will combine with =
mole of
Thus
is the limiting reagent as it limits the formation of product.
As 1 mole of
give = 1 mole of 
Thus 0.33 moles of
give =
of 
Mass of 
Thus theoretical yield (g) of
produced by the reaction is 9.9 grams