Select the option which is the most appropriate one word substitution for the given group of words.

A decision which cannot be taken back

irrevocable

The most appropriate option which is the one-word substitution for the given group of words "a decision which cannot be taken back" is irrevocable.

• Irrevocable means that cannot be changed, reversed, or recovered; final.
• Irrational means not logical or reasonable.
• Indelible means that cannot be removed.
• Infallible means absolutely trustworthy.

The word irrevocable is the most appropriate because it specifically refers to a decision that cannot be changed or reversed. The other words do not have the same connotation of being a decision that is final and cannot be undone.