Students practice determining the total number of atoms in chemical formulas like Ba(OH)2 and Mg(NO3)2 on this physical science worksheet.

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

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

Answer: 2

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2. H₂SO₄

- H: 2 atoms (from \( H_2 \))
- S: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total: \( 2 + 1 + 4 = 7 \)

Answer: 7

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3. KNO₃

- K: 1 atom
- N: 1 atom
- O: 3 atoms (from \( O_3 \))
- Total: \( 1 + 1 + 3 = 5 \)

Answer: 5

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4. CaCl₂

- Ca: 1 atom
- Cl: 2 atoms (from \( Cl_2 \))
- Total: \( 1 + 2 = 3 \)

Answer: 3

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5. C₂H₆

- C: 2 atoms (from \( C_2 \))
- H: 6 atoms (from \( H_6 \))
- Total: \( 2 + 6 = 8 \)

Answer: 8

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6. Ba(OH)₂

- Ba: 1 atom
- OH: 2 units (from \( (OH)_2 \))
- Each \( OH \) unit contains:
- O: 1 atom
- H: 1 atom
- Total atoms in 2 \( OH \) units: \( 2 \times (1 + 1) = 4 \)
- Total: \( 1 + 4 = 5 \)

Answer: 5

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7. NH₄Br

- N: 1 atom
- H: 4 atoms (from \( H_4 \))
- Br: 1 atom
- Total: \( 1 + 4 + 1 = 6 \)

Answer: 6

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8. Ca₃(PO₄)₂

- Ca: 3 atoms (from \( Ca_3 \))
- PO₄: 2 units (from \( (PO_4)_2 \))
- Each \( PO_4 \) unit contains:
- P: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total atoms in 2 \( PO_4 \) units: \( 2 \times (1 + 4) = 10 \)
- Total: \( 3 + 10 = 13 \)

Answer: 13

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9. Al₂(SO₄)₃

- Al: 2 atoms (from \( Al_2 \))
- SO₄: 3 units (from \( (SO_4)_3 \))
- Each \( SO_4 \) unit contains:
- S: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total atoms in 3 \( SO_4 \) units: \( 3 \times (1 + 4) = 15 \)
- Total: \( 2 + 15 = 17 \)

Answer: 17

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10. Mg(NO₃)₂

- Mg: 1 atom
- NO₃: 2 units (from \( (NO_3)_2 \))
- Each \( NO_3 \) unit contains:
- N: 1 atom
- O: 3 atoms (from \( O_3 \))
- Total atoms in 2 \( NO_3 \) units: \( 2 \times (1 + 3) = 8 \)
- Total: \( 1 + 8 = 9 \)

Answer: 9

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11. Cu(NO₃)₂

- Cu: 1 atom
- NO₃: 2 units (from \( (NO_3)_2 \))
- Each \( NO_3 \) unit contains:
- N: 1 atom
- O: 3 atoms (from \( O_3 \))
- Total atoms in 2 \( NO_3 \) units: \( 2 \times (1 + 3) = 8 \)
- Total: \( 1 + 8 = 9 \)

Answer: 9

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12. KMnO₄

- K: 1 atom
- Mn: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total: \( 1 + 1 + 4 = 6 \)

Answer: 6

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13. H₂O₂

- H: 2 atoms (from \( H_2 \))
- O: 2 atoms (from \( O_2 \))
- Total: \( 2 + 2 = 4 \)

Answer: 4

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14. H₃PO₄

- H: 3 atoms (from \( H_3 \))
- P: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total: \( 3 + 1 + 4 = 8 \)

Answer: 8

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15. (NH₄)₃PO₄

- NH₄: 3 units (from \( (NH_4)_3 \))
- Each \( NH_4 \) unit contains:
- N: 1 atom
- H: 4 atoms (from \( H_4 \))
- Total atoms in 3 \( NH_4 \) units: \( 3 \times (1 + 4) = 15 \)
- P: 1 atom
- O: 4 atoms (from \( O_4 \))
- Total: \( 15 + 1 + 4 = 20 \)

Answer: 20

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16. Fe₂O₃

- Fe: 2 atoms (from \( Fe_2 \))
- O: 3 atoms (from \( O_3 \))
- Total: \( 2 + 3 = 5 \)

Answer: 5

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17. NaC₂H₃O₂

- Na: 1 atom
- C: 2 atoms (from \( C_2 \))
- H: 3 atoms (from \( H_3 \))
- O: 2 atoms (from \( O_2 \))
- Total: \( 1 + 2 + 3 + 2 = 8 \)

Answer: 8

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18. Mg(C₂H₃O₂)₂

- Mg: 1 atom
- C₂H₃O₂: 2 units (from \( (C_2H_3O_2)_2 \))
- Each \( C_2H_3O_2 \) unit contains:
- C: 2 atoms (from \( C_2 \))
- H: 3 atoms (from \( H_3 \))
- O: 2 atoms (from \( O_2 \))
- Total atoms in 2 \( C_2H_3O_2 \) units: \( 2 \times (2 + 3 + 2) = 14 \)
- Total: \( 1 + 14 = 15 \)

Answer: 15

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19. Hg₂Cl₂

- Hg₂: 2 atoms (from \( Hg_2 \))
- Cl: 2 atoms (from \( Cl_2 \))
- Total: \( 2 + 2 = 4 \)

Answer: 4

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20. K₂SO₃

- K: 2 atoms (from \( K_2 \))
- S: 1 atom
- O: 3 atoms (from \( O_3 \))
- 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}