The correct answer is until.
The word “until” is used to indicate a point in time at which something will happen or be completed. In the sentence “I shall punish you until you apologize,” the word “until” indicates that the speaker will not punish the listener until the listener apologizes.
The word “unless” is used to indicate a condition that must be met before something will happen or be completed. In the sentence “I shall punish you unless you apologize,” the word “unless” indicates that the speaker will not punish the listener unless the listener does not apologize.
The word “till” is a synonym for “until.” It can be used in the same way as “until” to indicate a point in time at which something will happen or be completed. However, “till” is more informal than “until.”
The word “none of these” is not the correct answer because it does not make sense in the sentence. The sentence is about the speaker’s intention to punish the listener until the listener apologizes. The word “none of these” does not indicate a point in time or a condition that must be met.