The correct option is
C eclipse
Option A: 'Peregrination' means 'a journey or voyage'.
Option B: 'Accumulation' refers to 'a mass or quantity of something that has been gradually building up'.
Option C: 'Eclipse' refers to 'the downfall or decline of something or someone'.
Option D: 'Rebuttal' means 'a denial'.
Option E: 'Failure' means 'lack of something'.
From these words, 'eclipse' is most appropriate in meaning: 'Mohan's reputation was in eclipse/decline.
Hence option C is correct.
The other words do not contribute a relevant meaning to the sentence.
'Eclipse' is similar to 'failure' but the latter is not suitable in terms of wording: one is not 'IN failure', but one EXPERIENCES it.
Hence options A, B, D and E are wrong.