The number of protons in a negatively charged atom (anion) is

The atomic number of an element is defined by the number of protons in its nucleus [t1][t3]. In a neutral atom, the number of protons equals the number of electrons [t1][t5]. An anion is a negatively charged ion formed when an atom gains one or more electrons [c1][t8]. While the number of protons remains constant and equal to the atomic number during ion formation [t3][t8], the addition of electrons creates an imbalance where the total negative charge exceeds the total positive charge [t2][t10]. Consequently, in an anion, the number of protons is less than the number of electrons [c1][t4]. For example, a chloride anion (Cl–) has 17 protons (its atomic number) but 18 electrons [c2]. Therefore, while the proton count still matches the atomic number, it is strictly less than the electron count in a negatively charged state.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 25: Thunderstorm > 25.4. Lightning And Thunder > p. 348
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47
3. [3] https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:ions/v/introduction-to-ions
4. [4] https://www.energy.gov/science/doe-explainselectrons