What are the primary and the secondary valences of Ni in [Ni(NH3)6]Cl2, respectively?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2 and 6
In \( \ce{[Ni(NH3)6]Cl2} \) the six \( \ce{NH3} \) molecules are inside the coordination sphere and the two \( \ce{Cl^-} \) ions are outside it:
\( \displaystyle \ce{[Ni(NH3)6]Cl2 -> [Ni(NH3)6]^2+ + 2Cl^-} \)
Oxidation state of Ni: x + 6(0) = +2, so x = +2.
Primary valence: ionisable and satisfied by the two free \( \ce{Cl^-} \) ions, so it is 2 (equal to the oxidation state).
Secondary valence: non-ionisable and equal to the number of groups bound directly to Ni, the six \( \ce{NH3} \) molecules, so it is 6.
NCERT (2026-27 edition):
5.1 Werner’s Theory of Coordination Compounds – “2. The primary valences are normally ionisable and are satisfied by negative ions.”
“3. The secondary valences are non ionisable. These are satisfied by neutral molecules or negative ions. The secondary valence is equal to the coordination number and is fixed for a metal.”