Concept:The second military coup in Nigeria was a counter-coup carried out by Northern military officers to reverse the first coup.
Explanation:The first military coup in Nigeria took place on January 15, 1966.
It was led mainly by Igbo officers, and it led to the killing of many Northern and Western leaders.
On July 29, 1966, Northern army officers staged a retaliation coup, popularly called the "July Rematch".
This second coup removed the Head of State, General Aguiyi-Ironsi, who was killed during the event.
Therefore, the second military coup d'état in Nigeria occurred on July 29, 1966.
The other options are not correct because they either refer to later events or to the first coup date.
Answer:A. July 29, 1966.