When a neutral atom loses an electron from its outer shell, it becomes which of the following?

Introduction / Context:
Atoms are made up of positively charged protons and neutral neutrons in the nucleus, surrounded by negatively charged electrons. In a neutral atom, the number of protons equals the number of electrons, so the net charge is zero. When atoms lose or gain electrons, they become ions with a net positive or negative charge. This question asks you to identify what happens when a neutral atom loses an electron from its outer shell.

Given Data / Assumptions:

• Initially, the atom is neutral, so total positive charge equals total negative charge.
• One or more electrons are removed from the atom.
• The nucleus, containing protons and neutrons, remains unchanged in this process.
• We assume basic atomic structure knowledge from school chemistry or physics.

Concept / Approach:
The total charge of an atom is determined by the balance between positively charged protons and negatively charged electrons. Removing an electron decreases the amount of negative charge while leaving the positive charge unchanged. As a result, there is an excess of positive charge, and the atom becomes a positively charged ion, known as a cation. If an atom were to gain an electron instead, it would become a negatively charged ion, called an anion. Neutrons are uncharged and do not directly affect the net charge when electrons are lost or gained.

Step-by-Step Solution:
Step 1: Start from a neutral atom where the number of protons equals the number of electrons, making the net charge zero. Step 2: Consider the effect of losing one electron. The number of electrons decreases by one, so the negative charge decreases. Step 3: The nucleus still contains the same number of protons, so the total positive charge is unchanged. Step 4: With fewer electrons than protons, the net charge becomes positive, and the atom is now a positively charged ion. Step 5: Such positively charged ions are called cations, so the correct answer is that the atom becomes a positive ion.

Verification / Alternative check:
Consider a simple example such as a sodium atom with 11 protons and 11 electrons. In neutral form, its net charge is zero. If it loses one electron during a chemical reaction, it now has 11 protons and 10 electrons, giving a net charge of +1. This species is written as Na^+ and is called a sodium ion, a classic example of a cation formed by electron loss. Similar reasoning applies to many metals in ionic compounds, confirming that losing electrons produces positive ions.

Why Other Options Are Wrong:
A neutron: A neutron is a neutral particle inside the nucleus; losing an electron does not convert the atom into a neutron. A negative ion: A negative ion or anion forms when an atom gains electrons, not when it loses them. An unchanged neutral atom: Removing an electron changes the balance of charges, so the atom can no longer remain neutral.

Common Pitfalls:
Some learners get confused between losing and gaining electrons, reversing the sign of the resulting ion. A helpful tip is to recall that electrons are negative; losing negative charge leaves the atom with more positive charge, while gaining electrons adds negative charge. Another mistake is to think that changing electrons changes the element itself; in fact, the element identity is determined by protons, and only the ionisation state changes when electrons are added or removed.

Final Answer:
When a neutral atom loses an electron, it becomes a positive ion, also called a cation.