Respuesta :

The 3 outside means to multiply the inside by that number.  AL(NO2)3 has 
1 N inside
1 x 3 = 3 nitrogen atoms

The molar mass of Al(NO3)3= 212.996 g/mol
nitrogen is 14 g/mol and is 19.7% if the molar mass
19.7% of 12 g = 2.354g 
2.354/14 = 0.196 N 

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