Option 1: Swamy Vivekananda was a prominent Indian philosopher and spiritual leader who emphasized the importance of truth and knowledge. However, he did not specifically say that truth is the ultimate reality and God.

Option 2: Rabindra Nath Tagore was a renowned poet, writer, and philosopher in India. While he did address the concept of truth and spirituality in his works, he did not directly state that truth is the ultimate reality and God.

Option 3: M.K. Gandhi, also known as Mahatma Gandhi, was a key figure in India`s independence movement and a promoter of non-violence. He believed that truth and God are closely connected, and he often stated that truth (or "Satya") is God.

Option 4: Radhakrishnan, or Sarvepalli Radhakrishnan, was an Indian philosopher, statesman, and former President of India. Though he emphasized the importance of truth and knowledge, he did not specifically mention that truth is the ultimate reality and God.

Therefore, the correct answer is option 3, M.K. Gandhi, who said, "Truth is the ultimate reality, and it is God."