A sample of ammonia (NH3) contains 12 molecules. How many nitrogen atoms are present in the sample?
12 nitrogen atoms
The formula NH3 shows that one molecule of ammonia contains 1 nitrogen atom and 3 hydrogen atoms. So the number of nitrogen atoms in a sample = number of molecules × 1.
The sample has 12 molecules, so the number of nitrogen atoms = 12 × 1 = 12.
Check: the 12 molecules also contain 12 × 3 = 36 hydrogen atoms, so the total number of atoms is 12 + 36 = 48 = 12 × 4, which agrees with each NH3 molecule having 4 atoms.
Hence, 12 nitrogen atoms.
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