What is the number of nitrogen atoms in 12g aluminium nitrate, Al (NO3) 3?

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