Question

What is the oxidation number of Pt in PtCl$_6^{2-}$?

• A. +6
• B. +4
• C. -6
• D. -4

Hint:

Remember that the sum of oxidation states in a polyatomic ion equals the charge of the ion. Halogens usually have an oxidation state of $-1$ in compounds unless they are bonded to oxygen or a more electronegative halogen.

Answer 1

The Correct Option is A

Step 1: Identify the components and overall charge. The given complex ion is PtCl$_6^{2-}$. The overall charge of the complex ion is $-2$. Chlorine (Cl) is a halogen and typically has an oxidation number of $-1$ when it is part of a compound. There are six chlorine atoms in the complex.
Step 2: Set up the equation for oxidation numbers. Let $x$ be the oxidation number of Platinum (Pt). The sum of the oxidation numbers of all atoms in the complex ion must equal the overall charge. \[ x + (6 \times -1) = -2 \]
Step 3: Solve for the oxidation number of Pt. \[ x - 6 = -2 \] Add 6 to both sides of the equation: \[ x = -2 + 6 \] \[ x = +4 \] Thus, the oxidation number of platinum in the complex ion PtCl$_6^{2-}$ is $+4$.