Question

The oxidation states of potassium and each iodine in potassium tri-iodide are OA. 1, 1/3 OB. -1, 2/3 OC. 1, -1/3 OD. 1/3, -1 O E. 1, -3 OF. 1,-2/3 Reset Selection

Answer 1

Step 1: Explanation

Rule for assigning oxidation number

• The oxidation number of an element in its free (uncombined) state is zero -- for example, Al(s) or Zn(s).
• The oxidation number of a monatomic (one-atom) ion is the same as the charge on the ion --- for example: K+ ------> Oxidation number =+1
• The sum of all oxidation numbers in a neutral compound is zero.
• The sum of all oxidation numbers in a polyatomic  ion is equal to the charge on the ion.
• The oxidation number of alkali metal in a compound is usually +1.
• The oxidation state of hydrogen in a compound is usually +1.
• The oxidation number of fluorine is always –1. Chlorine, bromine, and iodine usually have an oxidation number of –1, unless they’re in combination with an oxygen or fluorine.

Step 2: Solution

KI3 ------> oxidation number of K = +1 and each iodine = -1/3

KI3 has a net charge of 0 and we just discussed that alkali metal ( like Na, K, Rb etc)  will usually have an oxidation number of +1

if the charge of the Iodine(I) be X

then , (+1) + X(3) = 0 => X = -1/3

So, the oxidation number of potassium(K) = +1 and each iodine = -1/3 ----> option(C)