Counting Atoms Practice worksheet for identifying coefficients and subscripts in chemical formulas.

Let’s go step by step to solve this problem.

We are given chemical formulas and asked to find:
- The coefficient (the number in front of the whole formula — if there’s no number, it means 1)
- The subscripts for each element (the small numbers after each element symbol — if there’s no subscript, it means 1)

Remember:
→ Coefficient = how many molecules or units you have
→ Subscript = how many atoms of that element are in ONE molecule

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Problem 1: 2MgCl₂

- Coefficient: There’s a “2” in front → coefficient = 2
- Subscript for Mg: No number after Mg → that means 1
- Subscript for Cl: There’s a “2” after Cl → subscript = 2

✔ So:
coefficient: 2
Subscript for Mg: 1
Subscript for Cl: 2

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Problem 2: V₅O₅

Wait — let’s look carefully. It says “V₅O₅”. But note: there is no number in front, so coefficient = 1.

Also, subscripts are written as small numbers after each element.

- Coefficient: Nothing in front → 1
- Subscript for V: “5” after V → 5
- Subscript for O: “5” after O → 5

✔ So:
coefficient: 1
Subscript for V: 5
Subscript for O: 5

*(Note: This might be a typo in real chemistry — vanadium pentoxide is usually V₂O₅ — but we’re going by what’s written here.)*

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Problem 3: 4K₂CO₃

- Coefficient: “4” in front → 4
- Subscript for K: “2” after K → 2
- Subscript for C: No number after C → 1
- Subscript for O: “3” after O → 3

✔ So:
coefficient: 4
Subscript for K: 2
Subscript for C: 1
Subscript for O: 3

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Problem 4: NaC₂H₃O₂

This one has no coefficient written → so coefficient = 1

Now break down the subscripts:

- Na: no subscript → 1
- C: has “2” → 2
- H: has “3” → 3
- O: has “2” → 2

*(Note: This is sodium acetate — often written as NaC₂H₃O₂ — yes, the O has subscript 2 at the end.)*

✔ So:
coefficient: 1
Subscript for Na: 1
Subscript for C: 2
Subscript for H: 3
Subscript for O: 2

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## Final Answer:

1) 2MgCl₂
- coefficient: 2
- Subscript for Mg: 1
- Subscript for Cl: 2

2) V₅O₅
- coefficient: 1
- Subscript for V: 5
- Subscript for O: 5

3) 4K₂CO₃
- coefficient: 4
- Subscript for K: 2
- Subscript for C: 1
- Subscript for O: 3

4) NaC₂H₃O₂
- coefficient: 1
- Subscript for Na: 1
- Subscript for C: 2
- Subscript for H: 3
- Subscript for O: 2