Identify least stable species from following.

Step-by-step solution

Electron-donating groups stabilize positively charged species through the +I effect, with alkyl groups providing increasing stabilization as their number increases. NH₄^+ lacks alkyl substituents and receives no inductive stabilization from electron-donating groups. R-NH₃+ gains modest stabilization from one alkyl group, while R₂NH₂^+ benefits more strongly from two alkyl groups. R₃NH^+ achieves maximum stability through three electron-donating alkyl groups. The stability order follows the number of alkyl substitue