When was Hajj made obligatory?

a) 7 Hijri

b) 8 Hijri

c) 9 Hijri

d) 10 Hijri

After conquest of Makkah in 8 AH, Hajj was made compulsory in 9th AH. Prophet Muhammad (PBUH) performed one Hajj. Hajj is obligatory for a Muslim who fulfills required condition for at least once in life.