Answer: Number of electrons.
- A Number of electrons
- B Number of protons
- C Atomic mass
- D Atomic number
Correct answer: A. Number of electrons
Explanation: Isoelectronic species (e.g., N<sup>3-</sup>, O<sup>2-</sup>, F-, Ne, Na+) have the same number of electrons but different nuclear charges.
The complete modern periodic table (118 elements). Image: Cepheus et al., Public Domain, via Wikimedia Commons.
Concept context
The periodic table organises all 118 elements by atomic number and similar properties. Study periodic trends like atomic radius, ionization energy, and electronegativity, and learn how an element's position predicts its behaviour.
Read the full Classification of Elements and Periodicity in Properties notes →