In atomic structure, the formation of a cation from a neutral atom occurs by which fundamental process?

Introduction / Context:
This question checks a basic but crucial idea in atomic structure and chemical bonding: how ions are formed from neutral atoms. Understanding the difference between cations and anions, and the processes that form them, is essential for predicting the behaviour of elements in reactions and in ionic compounds. Here, you must identify which process leads specifically to the formation of a positively charged ion, or cation.

Given Data / Assumptions:

• A neutral atom initially has equal numbers of protons and electrons.
• A cation is defined as a positively charged ion.
• The options describe gain or loss of electrons or protons.
• We assume that changes in the nucleus, such as gain or loss of protons, are not common in ordinary chemical reactions.

Concept / Approach:
The charge on an atom or ion is determined by the balance between positively charged protons in the nucleus and negatively charged electrons around the nucleus. In chemical processes, the number of protons in the nucleus remains fixed because changing protons would turn one element into another and requires nuclear reactions. However, atoms can readily gain or lose electrons. If an atom loses one or more electrons, it has more protons than electrons and becomes positively charged, forming a cation. If it gains electrons, it becomes negatively charged, forming an anion. Therefore, formation of a cation is associated with loss of electrons, not gain of electrons or change in proton number in ordinary chemistry.

Step-by-Step Solution:
Step 1: Start with a neutral atom where number of protons equals number of electrons, so overall charge is zero. Step 2: Consider what happens when the atom loses one electron. Now the number of protons exceeds the number of electrons by one. Step 3: Because protons are positively charged and outnumber electrons, the net charge of the particle becomes positive. This species is a cation. Step 4: If instead the atom gained an electron, the electron count would exceed the proton count, yielding a negatively charged anion. Step 5: Gaining or losing protons would change the atomic number and identity of the element, which does not occur in typical chemical processes. Step 6: Therefore, the correct description of cation formation is loss of an electron.

Verification / Alternative check:
Take the example of a sodium atom, which has 11 protons and 11 electrons in its neutral state. If sodium loses one electron, it now has 11 protons and 10 electrons. The net charge is plus one because there is one more positive charge than negative charge. This ion is written as Na+ and is a cation. Similarly, a magnesium atom with 12 protons and 12 electrons can lose two electrons to become Mg2+, with a net charge of plus two. In both cases, the process involved is loss of electrons with the proton count unchanged. This pattern confirms that cations are formed by electron loss.

Why Other Options Are Wrong:
Gain of an electron would produce an anion, not a cation, because the species would now have more negative charges than positive charges. Gain of a proton is not a typical process in chemical reactions, and if it occurs in nuclear reactions, it changes the element itself, not just its ionic state. Loss of a proton likewise is a nuclear process and not the general route for forming cations in chemistry. Therefore these options do not correctly describe the usual formation of a cation from a neutral atom.

Common Pitfalls:
Some students mistakenly think that adding a positive particle like a proton is the way to make a positive ion, but in chemistry courses, ions are usually formed by electron transfer, not by changing the nucleus. Another common error is to mix up cations and anions and forget which is positive and which is negative. A simple mnemonic is that cation contains the letter t, which looks like a plus sign, reminding you that cations carry a positive charge. Remember also that metals tend to form cations by losing electrons, while non metals tend to form anions by gaining electrons.

Final Answer:
A cation is formed from a neutral atom by the loss of an electron.