An atom is the:

Options

A. smallest particle of matter known
B. smallest particle of a gas
C. smallest particle of an element that can take part in a chemical change
D. radioactive emission.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the definition of an atom. We need to evaluate the given options to identify which one correctly defines an atom.

2. **Evaluating Option A**: The first option states that an atom is the "smallest part of matter known." While atoms are fundamental units of matter, there are subatomic particles (like protons, neutrons, and electrons) that are smaller than atoms. Therefore, this option is incorrect.

3. **Evaluating Option B**: The second option claims that an atom is the "smallest particle of gas." This is misleading because gases are made up of atoms, but an atom is not specifically defined as a particle of gas. Thus, this option is also incorrect.

4. **Evaluating Option C**: The third option states that an atom is the "smallest particle of an element that can take part in a chemical change." This definition accurately describes an atom, as it is indeed the smallest unit of an element that retains the properties of that element and can participate in chemical reactions. Therefore, this option is correct.

5. **Evaluating Option D**: The last option mentions "radioactive emission." This does not define an atom but rather refers to a process involving the decay of certain types of atoms. Hence, this option is incorrect.

6. **Conclusion**: After evaluating all the options, the correct answer is option C: "smallest particle of an element that can take part in a chemical change."

**Final Answer**: C) smallest particle of an element that can take part in a chemical change.

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