The question asks us to match the terms of Niyama (observations) with their correct descriptions. Let's analyze each term and its corresponding description:

1. Śauca: This term is associated with cleanliness or purity. In the context of Niyama, it refers to the purity of body, mind, and thought. This aligns with the description (I), "Purity of body, mind, thought."
2. Santoşa: This term is related to contentment and satisfaction—having a positive outlook and being content with what one has. Thus, it matches description (II), "Positive Contentment."
3. Tapas: This term refers to austerity, discipline, and self-control. It involves practices aimed at purifying the body and mind through self-discipline. Therefore, it matches description (IV), "Austerity."
4. Svādhyāya: This term refers to self-study and introspection, involving the process of knowing and understanding oneself through study and reflection. It is correctly described by (III), "Self-study, introspection."

Thus, the correct matching is:

• (A) - (I): Śauca - Purity of body, mind, thought
• (B) - (II): Santoşa - Positive Contentment
• (C) - (IV): Tapas - Austerity
• (D) - (III): Svādhyāya - Self-study, introspection

The correct answer according to the matches above is option: (A) - (I), (B) - (II), (C) - (IV), (D) - (III)

This completes the matching with proper understanding of each terminology used in the Niyamas.