A 5.00 g sample of an anhydrous Group II metal nitrate loses 3.29g in mass on strong heating.
Which metal is present?
A magnesium
B calcium
C strontium
D barium

Question

A 5.00 g sample of an anhydrous Group II metal nitrate loses 3.29g in mass on strong heating. 
Which metal is present? 
A  magnesium 
B  calcium 
C  strontium 
D  barium

jfraser · Answer

since it's a Group II nitrate, you know the formula must be $M(NO_3)_2$, and the residue left over is most likely the metal oxide, $MO$, so use the differences in mass to find the mass percent, then the mole percent, then the molar mass of the metal.