moles x molar mass = grams.
You have moles and grams, calculate molar mass.
I would subtract 48(3x16=48 for 3 atoms O) from the molar mass and divide the remainder by 2 to get the atomic mass of M and from there look on the periodic table for the element M.
moles O = moles M2O3 x (3 atoms O/1 mole M2O3).
Post your work if you get stuck.
A 0.370mol sample of a metal oxide (M2O3) weighs 55.4g.
How many moles of O?
How many grams of M?
And what is the unknown element M?
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