Step 1: Nature of Tripiṭaka.
The Tripiṭaka is a collection of Buddhist scriptures, comprising the Vinayapiṭaka, Suttapiṭaka, and Abhidhamma Piṭaka.
It contains the Buddha's teachings, explaining ethics, meditation, and Dharma.
Step 2: Subject matter.
The Tripiṭaka primarily focuses on the adherence to Saddharma, the practice of Dharma, sutras, Vinaya, and philosophical inquiry.
It guides individuals towards liberation and Nirvana.
Step 3: Analysis of options.
(1) Prakṛti–Puruṣa classification → This is the subject of Sāṁkhya philosophy, not the Buddhist Tripiṭaka.
(2) Kaivalya → This term is used for Jain and Sāṁkhya yoga, not in Buddhist doctrine.
(3) Saddharma → Absolutely correct. The Tripiṭaka is established for the practice and adherence to Saddharma.
(4) Happiness of life → This is a general objective, but the Tripiṭaka specifically focuses on the observance of Saddharma.
Step 4: Conclusion.
The correct answer to this question is (3) Performance of Saddharma.