Correct Answer: Constraint

Solution : The correct answer is the second option.

The word that is opposite in meaning to "abandon" is "constraint."

"Abandon" refers to the act of leaving something or someone entirely, often implying a lack of restraint or control whereas "constraint" refers to a limitation or restriction, implying a sense of control or confinement, which contrasts with the idea of abandonment.

The meanings of the other options are as follows:

Recklessness: It implies a lack of caution or consideration for consequences.

Casualness: It suggests an informal or relaxed approach, not necessarily a sense of abandonment.

Spontaneity: It refers to the quality of being spontaneous or acting on impulse, not necessarily implying abandonment.

Therefore, the correct antonym of the given word is constraint.