Select the most appropriate synonym of the word in brackets to fill in the blank.
Queen Gulnaar of Arabia mourned her ________ beauty. (waning)

The correct answer is fading.

Step-by-step Explanation:

1. Understand the given word:
The word given in brackets is waning. "Waning" means decreasing in vigor, strength, size, or intensity; becoming weaker or gradually diminishing (e.g., the waning moon or waning health/beauty).

2. Analyze the options:
• false: Not genuine; untrue or artificial. (Incorrect synonym)
• frightening: Causing fear or dread; terrifying. (Incorrect synonym)
• fading: Gradually growing faint, losing brightness, vitality, or strength; diminishing. (Correct synonym)
• futile: Producing no useful result; pointless or ineffective. (Incorrect synonym)

3. Conclusion:
Since both "waning" and "fading" describe something that is gradually decreasing or losing its former intensity/beauty, fading is the most appropriate synonym to complete the sentence.