The best answer to the question about the irony behind Danforth’s reasoning for refusing to pardon the remaining prisoners or postpone their hangings in Act 4 of "The Crucible" is:
b. It is ironic that his idea of justice extends more to those who have already been hanged than to those who are still alive.
This highlights Danforth's warped sense of justice, as he prioritizes the integrity of the court and the previous executions over the lives of the remaining prisoners, demonstrating a profound irony in his reasoning.