The atomic number of lead is 82. Its mass number is 207. How many protons, neutrons, and electrons does this atom of lead contain?

A. 207 protons, no neutrons, and 207 electrons
B. 125 protons, 82 neutrons, and 125 electrons
C. 82 protons, 125 neutrons, and 82 electrons
D. 82 protons, 207 neutrons, and 82 electrons

Sure, let's solve this step by step:

1. Identify the Atomic Number and Mass Number:
- The atomic number of lead (Pb) is 82.
- The mass number of lead is 207.

2. Find the Number of Protons:
- The number of protons in an atom is equal to its atomic number.
- Therefore, the number of protons in lead is 82.

3. Find the Number of Electrons:
- In a neutral atom, the number of electrons is equal to the number of protons.
- Therefore, the number of electrons in lead is also 82.

4. Find the Number of Neutrons:
- The number of neutrons can be found by subtracting the atomic number from the mass number.
- Number of neutrons = Mass number - Atomic number.
- Number of neutrons = 207 - 82 = 125.

Putting it all together, an atom of lead contains:
- 82 protons
- 125 neutrons
- 82 electrons

Thus, the correct answer is:
Option C: 82 protons, 125 neutrons, and 82 electrons.