Which of the following is not an autobiography?

The correct option is Patrick White: A Life.

An autobiography is a self-written account of a person's life. To determine which of the given options is not an autobiography, we can analyze each work:
1. Patrick White: A Life is a biography of the Nobel Prize-winning Australian author Patrick White, written by the biographer David Marr. Since it was written by someone else, it is a biography, not an autobiography.
2. Long Walk to Freedom is the famous autobiography written by Nelson Mandela, the former President of South Africa.
3. My Experiments with Truth (specifically, The Story of My Experiments with Truth) is the autobiography of Mahatma Gandhi.
4. Akkarmashi (The Outcaste) is a landmark autobiographical work by Sharankumar Limbale, detailing his struggles as a Dalit in India.

Therefore, Patrick White: A Life is the only work among the choices that is not an autobiography.