relative atomic mass
1. the ratio is as follows:
A(Co)/%Co=A(O)/%O => A(Co)=%Co*A(O)/%O
I calculated 58.76 if no mistakes
2. the same calculation
3. you must take into account that are 6 chlorine atoms in the molecule (you must divide by 6)
4. is a little more complex, but you have to observe that it is a combination reaction, i.e. all X react with all oxygen and the oxide is 3.72+4.8 = 8.52 g of X4O10. finally you must divide X by 4 and O by 10.
Good luck
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