The correct option is A Disintegration, enthused
The given sentence focuses on an action '______ of the party came to a halt' and its positive result 'a new sense of hope and purpose _______ rank and file of the Congress'.
Option B: 'Disintegration' means 'the process of losing cohesion or strength'.
'Enthused' means 'to express eager enjoyment or interest'.
These words are the most suitable, as they complete the meaning of the sentence:
The party had stopped disintegrating (getting worse) and because of that the rank and file (ordinary members) of the Congress throughout the country became motivated with a sense of hope and purpose.
Hence option B is correct.
Option A: 'Democracy' is a system of government that is elected by the people.
'Frenzy' is a state of uncontrolled, wild behaviour.
Option C: 'Experimentation' is 'an action of trying out new ideas or methods'.
'Jettisoned' means 'to abandon or discard'.
Option D: 'Agitation' means 'a state of anxiety'.
'Aggravated' means 'to have been made more serious or severe'.
These words do not form a statement complete in meaning.
Hence A, C and D are incorrect.