How many ions are produced in aqueous solution by one formula unit of [Pt(NH3)6]Cl4?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 5 ions
In water a complex salt ionises only into its coordination sphere (the square bracket, which stays together as one ion) and its counter ions (written outside the bracket). The ligands inside the bracket are not released.
Counter ions: four \( \ce{Cl^-} \) outside the bracket carry a total charge of −4: 4 ions.
Complex ion: to balance them the coordination sphere carries +4 (\( \ce{NH3} \) is neutral, so Pt is +4): \( \ce{[Pt(NH3)6]^4+} \), 1 ion.
\( \displaystyle \ce{[Pt(NH3)6]Cl4 -> [Pt(NH3)6]^4+ + 4Cl^-} \)
Total = 1 + 4 = 5 ions per formula unit.
NCERT (2026-27 edition):
5.2 Definitions of Some Important Terms Pertaining to Coordination Compounds – “The central atom/ion and the ligands attached to it are enclosed in square bracket and is collectively termed as the coordination sphere. The ionisable groups are written outside the bracket and are called counter ions.”