Final answer:
Nelson Mandela's tone in his persuasive speech to the youth in April 1990 can be best described as 'sincere and inspirational', emphasizing respect for the youth's role and contributions in the struggle against apartheid and promoting a united democratic future.
Step-by-step explanation:
The best description of Nelson Mandela's tone in his April 1990 speech is 'sincere and inspirational'. Mandela's words reflect a deep respect for the contributions and sacrifices of the youth in the struggle against apartheid. He addresses them as the backbone and the pride of the nation's people, emphasizing their courage, determination, and vital role in the movement. With the context of South Africa's history in mind, Mandela's speech is framed around the recognition of the youth's efforts and the continuous fight for a democratic and just society. The mention of political maturity and united action clearly aligns with his vision of an inclusive future for South Africa, free from the grasp of apartheid, which he passionately fought for during his time with the African National Congress (ANC) and throughout his presidency after being released from prison.