Least hard questions at the end of exam (7)
I believe the answer is:
softest
'least hard' is the definition.
('soft' is the opposite of 'hard' so 'softest' should be a synonym for 'least hard')
'questions at the end of exam' is the wordplay.
'at the end' suggests the final letters.
'exam' becomes 'test' (synonyms).
The final letter of 'questions' is 's'.
's'+'of'+'test'='SOFTEST'
(Other definitions for softest that I've seen before include "Least hard or rough" , "Most delicate or most lenient" , "Lowest in volume" , "most weak" .)