Correct Answer:
B. 9 Zil-Hajj
The correct answer is 9 Zil-Hajj. The gathering at Arafat, known as 'Wuquf al-Arafat', is the most crucial and indispensable pillar of Hajj. Pilgrims spend the entire day of the 9th of Zil-Hajj from noon until sunset in prayer and supplication on the plains of Arafat, seeking Allah's forgiveness and mercy.
8 Zil-Hajj is the day pilgrims move from Makkah to Mina.
10 Zil-Hajj is Eid al-Adha, when pilgrims perform the ritual of sacrifice and circumambulate the Kaaba.
11 Zil-Hajj is one of the days of Tashreeq, involving the ritual of stoning the pillars in Mina.
The day of Arafat is central to the Hajj pilgrimage's validity.