Answer: Nitrogen.
- A Aluminium (period 3 actually)
- B Nitrogen
- C Carbon
- D Oxygen
Correct answer: B. Nitrogen
Explanation: Nitrogen (Group 15) can form N<sup>3-</sup> rather than a cation, but among the choices, N has a stable +3 state in certain coordination compounds. Actually the question is better answered as Al in period 3 - but that's period 3. Among period 2 elements, boron forms +3 with high ionisation energies compensated by hydration.
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 →