Which is not a problem nigeria has faced post-independence? corrupt government officials increased disputes between the muslims in the north and the christians in the south depletion of its oil reserves political unrest as members of the various ethnic groups jostle for political control

Corrupt government officials - this was the case

Increased disputes between the Muslims in the North and the Christians in the South - this was the case

Depletion of its oil reserves  - This is the correct answer. In fact the oil reserves of Nigeria started suffering depletion in 21 Century, but oil exports are still the basis of its export (almost 80%)

Political unrest as members of the various ethnic groups jostle for political control  - this was the case and included persecition of the Igbo people.