Originally Posted by El Dorado
A. 40. The evolution applies to a single attack.
"Reach (Ex): One of an eidolon's attacks is capable of striking at foes at a distance. Pick one attack. The eidolon's reach with that attack increases by 5 feet."
The question then is “claws” a attack or two attacks? Since the term ‘attack” applies to both plural of the same type and singular, simply quoting the RAW does not answer the question.