Out of the following given statements, identify the correct ones :
(A) Yttrium does not exhibit variable oxidation states, yet it is a transition element.
(B) Many compounds of transition elements act as catalysts in various chemical reactions.
(C) Technetium is an artificially synthesized element of 4d transition series.
(D) The E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺.
Choose the correct answer from the options given below :

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.