Worksheet for students to practice calculating the number of atoms in various chemical formulas.

To determine the number of atoms in each chemical formula, we need to carefully analyze the subscripts and parentheses. Here's the step-by-step solution for each formula:

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1. NaCl

- Sodium (Na): 1 atom
- Chlorine (Cl): 1 atom
- Total: \( 1 + 1 = 2 \)

Answer: 2

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2. H₂SO₄

- Hydrogen (H): 2 atoms
- Sulfur (S): 1 atom
- Oxygen (O): 4 atoms
- Total: \( 2 + 1 + 4 = 7 \)

Answer: 7

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3. KNO₃

- Potassium (K): 1 atom
- Nitrogen (N): 1 atom
- Oxygen (O): 3 atoms
- Total: \( 1 + 1 + 3 = 5 \)

Answer: 5

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4. CaCl₂

- Calcium (Ca): 1 atom
- Chlorine (Cl): 2 atoms
- Total: \( 1 + 2 = 3 \)

Answer: 3

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5. C₂H₆

- Carbon (C): 2 atoms
- Hydrogen (H): 6 atoms
- Total: \( 2 + 6 = 8 \)

Answer: 8

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6. Ba(OH)₂

- Barium (Ba): 1 atom
- Oxygen (O): \( 2 \times 1 = 2 \) atoms (from 2 OH groups)
- Hydrogen (H): \( 2 \times 1 = 2 \) atoms (from 2 OH groups)
- Total: \( 1 + 2 + 2 = 5 \)

Answer: 5

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7. NH₄Br

- Nitrogen (N): 1 atom
- Hydrogen (H): 4 atoms
- Bromine (Br): 1 atom
- Total: \( 1 + 4 + 1 = 6 \)

Answer: 6

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8. Ca₃(PO₄)₂

- Calcium (Ca): \( 3 \) atoms
- Phosphorus (P): \( 2 \times 1 = 2 \) atoms (from 2 PO₄ groups)
- Oxygen (O): \( 2 \times 4 = 8 \) atoms (from 2 PO₄ groups)
- Total: \( 3 + 2 + 8 = 13 \)

Answer: 13

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9. Al₂(SO₄)₃

- Aluminum (Al): \( 2 \) atoms
- Sulfur (S): \( 3 \times 1 = 3 \) atoms (from 3 SO₄ groups)
- Oxygen (O): \( 3 \times 4 = 12 \) atoms (from 3 SO₄ groups)
- Total: \( 2 + 3 + 12 = 17 \)

Answer: 17

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10. Mg(NO₃)₂

- Magnesium (Mg): \( 1 \) atom
- Nitrogen (N): \( 2 \times 1 = 2 \) atoms (from 2 NO₃ groups)
- Oxygen (O): \( 2 \times 3 = 6 \) atoms (from 2 NO₃ groups)
- Total: \( 1 + 2 + 6 = 9 \)

Answer: 9

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11. Cu(NO₃)₂

- Copper (Cu): \( 1 \) atom
- Nitrogen (N): \( 2 \times 1 = 2 \) atoms (from 2 NO₃ groups)
- Oxygen (O): \( 2 \times 3 = 6 \) atoms (from 2 NO₃ groups)
- Total: \( 1 + 2 + 6 = 9 \)

Answer: 9

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12. KMnO₄

- Potassium (K): \( 1 \) atom
- Manganese (Mn): \( 1 \) atom
- Oxygen (O): \( 4 \) atoms
- Total: \( 1 + 1 + 4 = 6 \)

Answer: 6

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13. H₂O₂

- Hydrogen (H): \( 2 \) atoms
- Oxygen (O): \( 2 \) atoms
- Total: \( 2 + 2 = 4 \)

Answer: 4

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14. H₃PO₄

- Hydrogen (H): \( 3 \) atoms
- Phosphorus (P): \( 1 \) atom
- Oxygen (O): \( 4 \) atoms
- Total: \( 3 + 1 + 4 = 8 \)

Answer: 8

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15. (NH₄)₃PO₄

- Nitrogen (N): \( 3 \times 1 = 3 \) atoms (from 3 NH₄ groups)
- Hydrogen (H): \( 3 \times 4 = 12 \) atoms (from 3 NH₄ groups)
- Phosphorus (P): \( 1 \) atom
- Oxygen (O): \( 4 \) atoms
- Total: \( 3 + 12 + 1 + 4 = 20 \)

Answer: 20

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16. Fe₂O₃

- Iron (Fe): \( 2 \) atoms
- Oxygen (O): \( 3 \) atoms
- Total: \( 2 + 3 = 5 \)

Answer: 5

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17. NaC₂H₃O₂

- Sodium (Na): \( 1 \) atom
- Carbon (C): \( 2 \) atoms
- Hydrogen (H): \( 3 \) atoms
- Oxygen (O): \( 2 \) atoms
- Total: \( 1 + 2 + 3 + 2 = 8 \)

Answer: 8

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18. Mg(C₂H₃O₂)₂

- Magnesium (Mg): \( 1 \) atom
- Carbon (C): \( 2 \times 2 = 4 \) atoms (from 2 C₂H₃O₂ groups)
- Hydrogen (H): \( 2 \times 3 = 6 \) atoms (from 2 C₂H₃O₂ groups)
- Oxygen (O): \( 2 \times 2 = 4 \) atoms (from 2 C₂H₃O₂ groups)
- Total: \( 1 + 4 + 6 + 4 = 15 \)

Answer: 15

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19. Hg₂Cl₂

- Mercury (Hg): \( 2 \) atoms
- Chlorine (Cl): \( 2 \) atoms
- Total: \( 2 + 2 = 4 \)

Answer: 4

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20. K₂SO₃

- Potassium (K): \( 2 \) atoms
- Sulfur (S): \( 1 \) atom
- Oxygen (O): \( 3 \) atoms
- Total: \( 2 + 1 + 3 = 6 \)

Answer: 6

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Final Answers:

1. 2
2. 7
3. 5
4. 3
5. 8
6. 5
7. 6
8. 13
9. 17
10. 9
11. 9
12. 6
13. 4
14. 8
15. 20
16. 5
17. 8
18. 15
19. 4
20. 6

\boxed{2, 7, 5, 3, 8, 5, 6, 13, 17, 9, 9, 6, 4, 8, 20, 5, 8, 15, 4, 6}