Hi aspirant,

The oxidation state is a number assigned to an element in chemical combination which represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound.

In case of your compound the elements are:

• K with +1 oxidation state
• Cl with -1 oxidation state
• OH with -1 oxidation state

Now we can calculate the oxidation state of Ru as:

2*1+(OS of Ru)+1*(-1)+(-1)*5=0

=> (OS of Ru) -4=0

=> OS of Ru =4

Hope this helps.