Unity of thought and action has been the basis of India's strength and stability.

Answer: Option B

Unity : the state of being united or joined as a whole.
Bias : inclination or prejudice for or against one person or group, especially in a way considered to be unfair.
Diversity : the state of being diverse.
Division : the action of separating something into parts or the process of being separated.
Weakness : the state or condition of being weak.

Antonym of Unity is Diversity