Which of the following propositions is the obverse and logically equivalent to the proposition 'No umpires are partisans'?

The obverse is "All umpires are non-partisans", logically equivalent to the original.

Obversion first changes the quality, turning the E proposition into an affirmative A.

It then replaces the predicate with its complement, so partisans becomes non-partisans.

"No umpires are partisans" thus yields "All umpires are non-partisans".

Since obversion is always valid, the two propositions are logically equivalent.