An atom of silicon has a mass number of 29. How many neutrons does it have?

• (A) 14
• (B) 15
• (C) 16
• (D) 28
• (E) 29

To determine the number of neutrons in an atom of silicon with a mass number of 29, we first need to understand a few key concepts about atomic structure. The mass number of an atom is the total count of protons and neutrons in its nucleus. Silicon has an atomic number of 14, which tells us that it has 14 protons. The relationship between protons, neutrons, and mass number can be expressed with a simple formula:

The Formula for Neutrons

The number of neutrons can be calculated using the following equation:

Number of Neutrons = Mass Number - Atomic Number

Applying the Formula

In this case, we know:

• Mass Number = 29
• Atomic Number (number of protons) = 14

Now, substituting these values into our formula gives us:

Number of Neutrons = 29 - 14

Calculating this results in:

Number of Neutrons = 15

Conclusion

Therefore, an atom of silicon with a mass number of 29 contains 15 neutrons. The correct answer is (B) 15. This understanding of atomic structure is fundamental in chemistry and helps explain various properties of elements, including their behavior in reactions and their isotopes.