Correct Answer: Reassure

Solution : The correct choice is the fourth option .

Explanation: In this context, the term frighten refers to causing fear or making someone afraid. Among the options provided, reassure is the correct antonym, as it means to do the opposite, to provide comfort, ease, or confidence to counteract fear or anxiety.

The meanings of the other words are:

• Startle : It means to cause someone to feel a sudden shock or surprise, often leading to a brief moment of fear or alarm.
• Petrify : This term means to paralyse with fear or to make someone so frightened that they become immobilised as if turned to stone.
• Alarm : It refers to causing fear or anxiety, often sudden or unexpected, typically due to a perceived threat or danger.

So, the right antonym for the given question is reassure .