Potassium Dichromate or Potassium Permanganate?

Potassium dichromate - http://en.wikipedia.org/wiki/Potassium_dichromate

Potassium permanganate- http://en.wikipedia.org/wiki/Potassium_permanganat...

The most obvious difference is probably the colour, and thats because of different absorbance of light from the atoms.

Potassium Permanganate Wiki

I do not think oxidation number is a factor influencing oxidizing power. Oxidation power depends on the ion's ability to accept electrons (in the oxidizing agent). Anyway, Potassium Permanganate is a more powerful oxidizing agent than potassium dichromate as Manganate (VII) has a higher standard electrode potential value (+1.52V) than Dichromate (VI) (at +1.33V), both in an acidic medium.

Both are powerful oxidants, but typically if one can use manganate you do so with preference over chromate. Chromate is dangerously toxic stuff. In the lab there is typically a Chromate waste pot.

dichromate is +6 oxidation state, and this rapidly converts to chromate +5 which is one of the most powerful inorganic carcinogens.

On the other hand, manganese is not that bad. Not nice, but nowhere near that bad.

potassium dichromate is K2Cr2O7

WHEREAS

potassium permanganate is KMnO4

its colour ,reactions etc all differ

K2Cr2O7, KMnO4

Colour

loads of stuff.