Correct Answer: Exactly

Solution : The correct option is the first option.

Explanation:
Approximately means close to but not precisely accurate. Its antonym, exactly, signifies precision and accuracy without any deviation or approximation.

The meanings of the other options are as follows:

• Vaguely means indistinctly or unclearly.
• Hourly means occurring every hour.
• Truly refers to a manner that is genuine or per reality.

Therefore, the correct answer is exactly.