Correct Answer: implacable

Solution : The correct choice is the first option.

Explanation: The word implacable means unable to be appeased or pacified, indicating a strong and unyielding hostility. In the context of the sentence, where the man is supposed to be protecting but is described as the fiercest and most implacable enemy , it emphasises the paradoxical nature of the situation—someone who should provide protection is instead the most unrelenting adversary.

The meanings of the other options are as follows:

• Pedestrian : It means lacking inspiration or dull.
• Ostentatious : It means showy or pretentious.
• Quotidian : It means ordinary or everyday.

So, the correct sentence would be: "The man who is supposed to be protecting them is somehow their fiercest and most implacable enemy."