An iron atom (Fe) has 26 protons in its nucleus. How many electrons are present in an Fe2+ (iron II) ion formed from this atom?

Introduction / Context:
Understanding how ions form from neutral atoms is a basic skill in chemistry. When an atom gains or loses electrons, it becomes an ion with a positive or negative charge. The number of protons in the nucleus stays constant, because that defines the element. This question focuses on an iron atom that forms a doubly charged positive ion, Fe2+, and asks for the number of electrons in that ion, given that neutral iron has 26 protons.

Given Data / Assumptions:

• Neutral iron (Fe) has 26 protons in its nucleus.
• In a neutral atom, the number of electrons equals the number of protons.
• The ion of interest is Fe2+, which carries a positive charge of plus two.
• A positive charge indicates that electrons have been lost compared to the neutral atom.

Concept / Approach:
For a neutral atom, the number of electrons equals the atomic number, which is the number of protons. When an atom becomes a cation (positive ion), it does so by losing electrons. The magnitude of the positive charge tells us how many electrons have been lost. For Fe2+, the charge is plus two, which means the ion has lost two electrons compared to the neutral iron atom. Therefore, the number of electrons in Fe2+ equals 26 minus 2, which is 24. The proton count remains 26 and does not change when the ion forms.

Step-by-Step Solution:
Step 1: Start with the neutral iron atom, which has 26 protons and, therefore, 26 electrons. Step 2: Recognise that a Fe2+ ion has a charge of plus two, indicating that it has lost two negatively charged electrons. Step 3: Subtract the number of electrons lost from the original electron count: 26 minus 2. Step 4: Calculate 26 minus 2, which equals 24 electrons remaining in the ion. Step 5: Identify 24 as the correct answer among the given options.

Verification / Alternative check:
You can cross check the logic by thinking about charge balance. Protons are positively charged, electrons are negatively charged, and neutrons are neutral. In Fe2+, the net charge is plus two. If the ion has 26 protons and 24 electrons, the net charge is 26 positive minus 24 negative, which is plus two. This matches the notation Fe2+. If the ion had 26 electrons, it would be neutral, and if it had more than 26 electrons, it would be negatively charged. Therefore the count of 24 electrons is consistent with the symbol and the basic charge calculation.

Why Other Options Are Wrong:
- 26: This would mean the ion still has the same number of electrons as the neutral atom and would therefore be neutral, not Fe2+.
- 28: This would give the ion more electrons than protons, resulting in a negative ion, not a doubly positive cation.
- 13: This is far too low and would give a very high positive charge that does not match the Fe2+ symbol.
- 18: This would give a net charge of plus eight (26 minus 18), which again does not match the charge of plus two in Fe2+.

Common Pitfalls:
A common mistake is to confuse the number of protons with the ionic charge and subtract the charge from the proton count instead of the electron count. Another error is to forget that the atomic number, and therefore the number of protons, does not change when ions form. Keeping the simple rule in mind that positive charge means electrons have been lost and that the charge indicates how many has been lost helps to avoid such confusion.

Final Answer:
An Fe2+ ion has 24 electrons.