How many electrons does an atom with an atomic number of 20 and a mass number of 42 have?

Options

A. 20
B. 22
C. 42
D. 62

Answer

To determine how many electrons are present in an atom with an atomic number of 20 and a mass number of 42, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Atomic Number**: The atomic number of an element is defined as the number of protons in the nucleus of an atom. In this case, the atomic number is 20.

2. **Identify the Number of Protons**: Since the atomic number is 20, this means that the atom has 20 protons.

3. **Determine the Nature of the Atom**: For a neutral atom (which is the case here unless specified otherwise), the number of electrons is equal to the number of protons. This is because the positive charge of protons is balanced by the negative charge of electrons.

4. **Calculate the Number of Electrons**: Since the atom has 20 protons, it will also have 20 electrons to maintain electrical neutrality.

5. **Conclusion**: Therefore, the atom with an atomic number of 20 has 20 electrons.

### Final Answer:
The atom has **20 electrons**.

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