Ambiguity of thoughts can prove disastrous.

Answer: Option B

Ambiguity : the quality of being open to more than one interpretation; inexactness.
Rigidity : inability to be to bent or be forced out of shape.
Clarity : the quality of being coherent and intelligible.
Certainty : firm conviction that something is the case.
Rationality : the quality of being based on or in accordance with reason or logic.

Antonym of Ambiguity is Clarity