Redox, wrong Qs Cognito quiz

I got this wrongas i thought it was +6 as i forgot to total the oxidation number to -1 as its an ION.

REmemebr must total the ions total oxidation number

Asm miss to go thru

ask miss how to know ans, is it just trial and error

I didnt even watse time solving this one

Faster method:

-as its redox electrons must be before arrow due to red→ox,

and chargers muts balance on ecah side