Final answer:
Each formula unit of tourmaline contains a total of 31 oxygen atoms, derived from the addition of oxygen atoms in BO3, Si6O18, and OH groups in its chemical formula.
Step-by-step explanation:
The question asks to determine the number of oxygen atoms in each formula unit of the mineral tourmaline, with the chemical formula NaMgAl6(BO3)3Si6O18(OH)4. To find this, we need to count the oxygen atoms in each part of the formula:
- BO3 units: 3 oxygens × 3 units = 9 oxygen atoms
- Si6O18: 18 oxygen atoms
- (OH)4: 4 oxygen atoms
Adding these together: 9 (from BO3) + 18 (from Si6O18) + 4 (from OH) = 31 oxygen atoms.
Therefore, the correct answer is E. 31.