The unusually high value for Co is because of it's third ionization energy. Just remember that Co has the highest value. If you do it by electronic configuration, you won't get it. So better remember it
its just that Co2+ has a higher CFSE value than Co3+.. leading to greater stability of Co2+ than Co3+
Oh okay thanks
But if you are unaware of the answer,then how would you wether to apply CFT or go with electronic configuration?
You get the wrong answer by configuration. Just remember that Co is highest.
But that would just be one case Specifically for +3 to +2 ,in general like it's a mains question with no mention in ncert so I expected it to be something logical
In this type of questions, the logic that you apply is very simple which is that you just have to see that which can be easily reduced from +3 to +2 state, which means that +2 oxidation state is more stabe than +3 or the elements should be strong oxidizing agent. So now,you look into your options, greater the value of standard reduction potential in positive numbers, greater is the tendency to reduce.
So that will be your correct answer. In this case,Co is the correct answer.