Ulterior object behind an act is known as 

Motive

The correct answer is Option (4) → Motive

The motive refers to the ulterior object or reason behind an action. It is the driving force or reason that prompts an individual to act in a certain way. The criminal law does not take into account motive in affixing criminal liability or in determining criminal culpability. This is the reason why the criminal law does not care whether one has stolen a loaf of bread to fed a starving person or stolen medicine to save someone's life, as long as it is a prohibited act, done knowingly.

While intention is the immediate decision to bring about a certain result, motive is the underlying reason for the intention.

Mens rea refers to the guilty mind or criminal intent behind a wrongful act, and mistake refers to a misunderstanding or error in action or judgment.