The number of ions produced by one formula unit of [Pt(NH3)5Br]Br3 in aqueous solution is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 4
In water, the ligands inside the square bracket stay bound to the metal; only the counter ions written outside the bracket ionise.
\( \displaystyle \ce{[Pt(NH3)5Br]Br3 -> [Pt(NH3)5Br]^3+ + 3Br^-} \)
Complex ion: \( \ce{[Pt(NH3)5Br]^3+} \) = 1 ion (the Br inside the bracket is a ligand and is not released).
Counter ions: the three Br outside the bracket = 3 \( \ce{Br^-} \) ions.
Total: 1 + 3 = 4 ions.
NCERT (2026-27 edition):
5.2 Definitions of Some Important Terms Pertaining to Coordination Compounds – “(e) Coordination sphere
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.”