The hybridisation of the nitrogen atom in the NO₃⁻ ion is:

1. Nitrogen is the central atom, surrounded by three oxygen atoms. 2. Count regions of electron density around it: three bonded oxygens and no lone pair on nitrogen. 3. Three regions require three hybrid orbitals, formed from one s and two p orbitals. 4. That is sp² hybridisation, giving the trigonal planar shape the nitrate ion actually has. 5. Assigning sp³ was the common error and would predict a pyramidal ion, which nitrate is not. _Source: NECTA ACSEE 2023 Chemistry 132/1, Question 3: Chemical Bonding_