The sentence presents a clear contrast. The crowd is making "entreaties," or pleas, to the judge. The judge, however, "remained implacable," meaning he was unyielding and unwilling to change his mind. He then handed down a "harsh" and "arbitrary" punishment.

For the crowd's pleas to contrast with the judge's harsh, unyielding nature, they must be asking for the opposite of a harsh punishment. They are pleading for a reduction in the severity of the punishment.
- A. justice: While the crowd might want justice, a punishment that is "arbitrary" (based on random choice or personal whim, rather than any reason or system) is the antithesis of justice. However, "justice" is too broad; the context specifically points to a plea to lessen the harshness of the punishment, not a general concept.
- B. mercy: This means compassion or forgiveness shown toward someone whom it is within one's power to punish or harm. This perfectly fits the plea to a judge to lessen a harsh sentence.
- C. clemency: This means mercy; lenience. This is a direct synonym for "mercy" and fits the context equally well.
- D. appeasement: This means the action or process of appeasing, or pacifying, someone by acceding to their demands. It's more about preventing conflict than showing compassion in a legal context.
- E. condemnation: This means the expression of strong disapproval; censure. This is the opposite of what the crowd is pleading for.
- F. partiality: This means unfair bias in favor of one thing or person compared with another. This is an inappropriate quality for a judge and not what a crowd would be publicly pleading for in this context.

Both mercy and clemency convey the plea for compassion and leniency, which contrasts directly with the judge's "implacable" nature and "harsh" punishment.