What is ironic about jems certainty that Tom Robinson will be acquitted?

Answer 1

Even though the evidence was 100% in favor of his innocence, the attitude of the townspeople was they wanted to lynch Tom Robinson, just because he was black. The trial was a mere formality to make his convection legal in the eyes of the law. They wanted to kill him, because he was black, and they were the type of people to lynch blacks, just for the fun of killing a black person.

Answer 2

It is ironic because the reader knows that despite the evidence in Tom Robinson's favor, the racial prejudice of the jury will likely lead to his conviction. Jem's certainty highlights the naivety of youth and the disparity between innocence and the harsh reality of the justice system in Maycomb.