Number of isotopes of carbon is :

Explanation

To determine the number of isotopes of carbon, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Isotopes**:
- Isotopes are variants of a chemical element that have the same number of protons (atomic number) but different numbers of neutrons, leading to different mass numbers.

2. **Identifying Carbon's Atomic Number**:
- Carbon has an atomic number of 6, which means it has 6 protons in its nucleus.

3. **Finding Isotopes of Carbon**:
- The isotopes of carbon are identified by their mass numbers (A), which is the sum of protons and neutrons in the nucleus.
- The known isotopes of carbon are:
- Carbon-12 (C-12): 6 protons and 6 neutrons (mass number = 12)
- Carbon-13 (C-13): 6 protons and 7 neutrons (mass number = 13)
- Carbon-14 (C-14): 6 protons and 8 neutrons (mass number = 14)

4. **Counting the Isotopes**:
- From the above information, we can conclude that there are three isotopes of carbon: C-12, C-13, and C-14.

5. **Final Answer**:
- Therefore, the number of isotopes of carbon is **3**.