Final answer:
The secret of sixteen-year-old Pi that is revealed is his practice of three religions: Hinduism, Christianity, and Islam, which comes as a surprise to his family and the leaders of the individual faiths.
Step-by-step explanation:
The secret of the sixteen-year-old Pi that is outed is d) His three religions. In the novel Life of Pi by Yann Martel, Piscine Molitor Patel, known as Pi, practices Hinduism, Christianity, and Islam simultaneously. This unconventional practice comes to light when his family and the religious leaders discover Pi has been participating in the rituals and teachings of all three religions. This revelation leads to a difficult and amusing conversation as each religious representative learns of Pi's eclectic spiritual life. He resists choosing one faith over the others, seeing value and beauty in all three.