Which statement is true for all atoms that are anions in basic atomic chemistry?

Introduction / Context:
This question checks the basic definition of an anion in chemistry. Atoms and ions are distinguished by their numbers of protons and electrons. A neutral atom has equal numbers of protons and electrons. When an atom gains or loses electrons, it becomes an ion and carries a net charge. Anions are negatively charged ions, and the question asks which statement must always be true for any anion, regardless of which element it comes from.

Given Data / Assumptions:

• An anion is a negatively charged ion.
• Protons carry positive charge and are located in the nucleus.
• Electrons carry negative charge and surround the nucleus.
• Neutrons are neutral and do not affect the net charge.
• The atomic number of an element equals the number of protons and does not change for ions of that element.

Concept / Approach:
The net charge on an ion is determined by the difference between the number of protons and electrons. For a neutral atom, protons and electrons are equal. An anion has a negative charge, which can only happen if there are more electrons (negative charges) than protons (positive charges). The number of neutrons can vary between isotopes but does not contribute to charge. Therefore, the universal property of all anions is an excess of electrons over protons, regardless of how many neutrons are present.

Step-by-Step Solution:
Step 1: Recall the definition of an anion. An anion is a negatively charged ion formed when an atom gains one or more electrons. Step 2: Relate charge to numbers of protons and electrons. Net charge = number of protons minus number of electrons. For the charge to be negative, electrons must outnumber protons. Step 3: Evaluate the statements. The only statement that must always hold is that the atom has more electrons than protons.

Verification / Alternative check:
Consider a chloride ion, Cl-. Neutral chlorine has 17 protons and 17 electrons. As Cl-, it has gained one extra electron, giving 17 protons and 18 electrons. This extra electron creates the negative charge and demonstrates that the anion has more electrons than protons. The same logic applies to oxide O2-, sulphide S2-, and other common anions. In each case, negative charge arises from extra electrons compared with the number of protons, confirming the general rule.

Why Other Options Are Wrong:
Option A: The number of protons compared with the neutral atom of the same element does not change; only the number of electrons changes, so this statement is false. Option B: Saying the atom has more protons than electrons would describe a positively charged ion or cation, not an anion. Option C: Having more neutrons than protons does not determine charge at all, so this cannot define an anion.

Common Pitfalls:
Students sometimes confuse cations and anions, mixing up which one gains or loses electrons. A simple memory aid is that anion starts with the letter a like in the word add, because an anion has added electrons. Confusing the role of neutrons is another issue; they can vary in number for isotopes but have no impact on charge. Always connect the sign of the charge directly with the balance between protons and electrons.

Final Answer:
For all anions, the true statement is that the atom has more electrons than protons.