In a sodium ion Na+, how many electrons are present around the nucleus?

Introduction / Context:
This basic chemistry question checks your understanding of how the number of electrons changes when a neutral atom forms a cation. It uses the sodium ion Na+ as a common example from ionic bonding and periodic table topics.

Given Data / Assumptions:

• We are dealing with the sodium ion, symbol Na+.
• Atomic number of sodium (Na) is 11.
• The ion has a single positive charge.
• We assume the ion is formed by loss of electrons, not by adding protons.

Concept / Approach:
The atomic number of an element equals the number of protons in its nucleus and also equals the number of electrons in the neutral atom. When a positive ion (cation) is formed, the atom loses one or more electrons. The charge on the ion tells you how many electrons have been lost or gained. For Na+, the plus one charge indicates that one electron has been lost relative to the neutral sodium atom. The number of protons does not change in this process.

Step-by-Step Solution:
1) Neutral sodium atom has atomic number 11, so it possesses 11 protons and 11 electrons.2) The ion Na+ has a charge of plus one.3) A plus one charge means the ion has one fewer electron than the neutral atom, because electrons carry negative charge.4) Therefore, electrons in Na+ = 11 (in neutral atom) minus 1 (lost) = 10 electrons.5) The number of protons remains 11, but the loss of one electron leads to a stable configuration similar to neon.

Verification / Alternative check:
We can cross check using the electron configuration. Neutral sodium has configuration 2, 8, 1. When it loses one electron to form Na+, the configuration becomes 2, 8, which totals 10 electrons. This is the same configuration as neon, a noble gas, explaining the stability of Na+ and confirming that the correct electron count is 10 in the sodium ion.

Why Other Options Are Wrong:
1: This would correspond to a hydrogen like ion and is far too low for sodium.
11: This is the number of electrons in neutral sodium, not in Na+ which has lost one electron.
12: This would imply an extra electron and describe Na- rather than Na+, which is not the ion in the question.
9: This would correspond to losing two electrons from sodium, giving a Na2+ ion, which is not common and not what is specified.

Common Pitfalls:
A common mistake is to confuse the number of electrons with the atomic number even for ions, forgetting that electrons can be lost or gained. Another error is to think that a positive charge indicates extra protons rather than fewer electrons. In reality, nuclear protons remain fixed in chemical changes; only electrons are transferred. Always adjust the electron count according to the ionic charge, keeping the proton count equal to the atomic number.

Final Answer:
The sodium ion Na+ contains 10 electrons around its nucleus.