Option 1 states that Nelson Mandela was the first President of South Africa. However, this is not true as Mandela was not the first President of South Africa. He did serve as the President of South Africa from 1994 to 1999, but he was not the first president.

Option 2 states that Mandela spent 18 years in prison on Robben Island. This statement is true. Nelson Mandela was imprisoned for 27 years, and a significant portion of this time was spent on Robben Island.

Option 3 states that Mandela became the President in 1990 after his release from prison. This statement is false. Nelson Mandela was released from prison in 1990 but did not become the President until 1994 when he won the first multi-racial elections in South Africa.

Given that option 3 is the only correct statement, the correct answer is option 3.

Alert - The correct answer should be option 2 and not option 3, as option 2 correctly states that Mandela spent 18 years in prison on Robben Island and became the President in 1994 after his release.