Atomic number is equal to the

Options

A. number of neutrons in the nucleus
B. number of protons in the nucleus
C. sum of protons and neutrons
D. atomic mass of the element

Explanation

To determine what the atomic number represents, we can follow these steps:

### Step 1: Understand the Definition of Atomic Number
The atomic number (denoted as Z) is defined as the number of protons in the nucleus of an atom.

### Step 2: Analyze the Options Given
The question provides several options:
1. Number of neutrons in the nucleus
2. Number of protons in the nucleus
3. Sum of protons and neutrons
4. Atomic mass of the element

### Step 3: Evaluate Each Option
- **Option 1**: Number of neutrons in the nucleus - This is incorrect because the atomic number specifically refers to protons, not neutrons.
- **Option 2**: Number of protons in the nucleus - This is correct, as the atomic number is defined as the number of protons.
- **Option 3**: Sum of protons and neutrons - This describes the atomic mass, not the atomic number.
- **Option 4**: Atomic mass of the element - This is also incorrect as atomic mass is the sum of protons and neutrons, not just protons.

### Step 4: Conclusion
From the evaluation, the correct answer is that the atomic number is equal to the number of protons in the nucleus.

### Final Answer
The atomic number is equal to the number of protons in the nucleus.

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