Question

An atom of lithium contains 3 electrons, 3 protons and 4 neutrons. Its mass number is:

• A. 3
• B. 4
• C. 7
• D. 10

Hint:

The mass number is the total count of nucleons (protons and neutrons). The number of electrons determines the charge, not the mass number.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the mass number of a lithium atom, given the number of its subatomic particles.
Step 2: Key Formula or Approach:
The mass number (\(A\)) of an atom is defined as the total number of protons (\(Z\)) and neutrons (\(N\)) in the nucleus.
\[ A = Z + N \] Step 3: Detailed Explanation:
From the problem statement, we have:
- Number of protons (\(Z\)) = 3
- Number of neutrons (\(N\)) = 4
- Number of electrons = 3
The number of electrons does not contribute to the mass number, as the mass of an electron is negligible compared to that of a proton or a neutron.
Using the formula for the mass number:
\[ A = 3 (\text{protons}) + 4 (\text{neutrons}) \] \[ A = 7 \] Step 4: Final Answer:
The mass number of the lithium atom is the sum of its protons and neutrons, which is 7.