Isotope | Practice | CK-12 Foundation - Free Printable

Let's solve the problem step by step based on the atomic structure diagrams and information provided.

We are given four atoms: Hydrogen-1, Carbon-?, Boron-11, and an unknown atom with atomic mass 3. We need to fill in the missing information for each atom: number of protons, neutrons, atomic mass, and element symbol (where needed).

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1. Hydrogen-1

Given:
- Symbol: H
- Atomic number (protons): 1
- Isotope: Hydrogen-1 → means atomic mass = 1

Protons: 1
Neutrons: Atomic mass - protons = 1 - 1 = 0
Atomic Mass: 1

✔ So, Hydrogen-1 has:
- Protons: 1
- Neutrons: 0
- Atomic Mass: 1

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2. Carbon-?

Given:
- Symbol: C
- Atomic number (protons): 6
- Electrons: 6 (since neutral atom)
- Number of neutrons: 6 (from diagram – orange dots in nucleus)

So, atomic mass = protons + neutrons = 6 + 6 = 12

Therefore, this is Carbon-12

Protons: 6
Neutrons: 6
Atomic Mass: 12

✔ So, Carbon-12 has:
- Protons: 6
- Neutrons: 6
- Atomic Mass: 12

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3. Boron-11

Given:
- Symbol: B
- Atomic number: 5 (from periodic table; also visible from electrons)
- Atomic mass: 11
- Protons: 5 (since atomic number = 5)

Neutrons: Atomic mass - protons = 11 - 5 = 6

✔ So, Boron-11 has:
- Protons: 5
- Neutrons: 6
- Atomic Mass: 11

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4. Unknown Atom

Given:
- Atomic mass: 3
- Protons: 2
- Electrons: 2 (from diagram)
- Element symbol: ?

From protons = 2 → This is Helium (He)

Neutrons: Atomic mass - protons = 3 - 2 = 1

So, this is Helium-3

✔ So, Helium-3 has:
- Protons: 2
- Neutrons: 1
- Atomic Mass: 3
- Element: He

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✔ Final Answers:

| Atom | Protons | Neutrons | Atomic Mass | Element |
|-------------|--------|----------|-------------|---------|
| Hydrogen-1 | 1 | 0 | 1 | H |
| Carbon-12 | 6 | 6 | 12 | C |
| Boron-11 | 5 | 6 | 11 | B |
| Helium-3 | 2 | 1 | 3 | He |

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🔍 Explanation:

- Atomic number = number of protons
- Atomic mass ≈ protons + neutrons
- In a neutral atom, protons = electrons
- The name of the element is determined by the number of protons.
- Isotopes have same protons but different neutrons.

So, the missing values are:

- Carbon: Atomic Mass = 12 → so it's Carbon-12
- Boron-11: Protons = 5
- Unknown: Element = Helium, symbol = He, Neutrons = 1

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🟩 Fill-in-the-blanks:

- Hydrogen-1:
- Protons: 1
- Neutrons: 0
- Atomic Mass: 1

- Carbon-?:
- Protons: 6
- Neutrons: 6
- Atomic Mass: 12 → So Carbon-12

- Boron-11:
- Protons: 5
- Neutrons: 6
- Atomic Mass: 11

- ?:
- Element: He
- Protons: 2
- Neutrons: 1
- Atomic Mass: 3

✔ All boxes can now be filled correctly.