The correct option is (a).
Explanation
During the Later Vedic period, the social structure became rigid and was organized into a fourfold Varna system as described by the priests (Brahmanas). This system defined the rights, duties, and status of individuals, marking a shift from the flexible social order of the Rig Vedic period to a hierarchy determined largely by birth.
Statement-wise Analysis
Statement 1 is Correct.
According to the Later Vedic texts, the first three varnas-Brahmanas, Kshatriyas, and Vaishyas-were considered dvija (twice-born). This status granted them the right to undergo the upanayana (sacred thread) ceremony. Consequently, both Kshatriyas and Vaishyas were eligible to study the Vedas and perform sacrifices (often as patrons or yajamanas), unlike the Shudras who were denied these rights.
Statement 2 is Incorrect.
While Shudras were indeed excluded from studying the Vedas and performing rituals, they were not the only group. In the Later Vedic period, the status of women deteriorated significantly. Women were often equated with Shudras in religious matters and were also explicitly excluded from studying the Vedas and performing Vedic rituals.
Statement 3 is Incorrect.
The Varna system described in the Later Vedic books was decided on the basis of birth, not occupation chosen in adulthood. While the Early Vedic society allowed for mobility based on profession, the Later Vedic society became stratified, and one's varna was determined by the family into which they were born.
Key Takeaway: The Later Vedic Varna system was a rigid, birth-based hierarchy where the first three varnas (Brahmanas, Kshatriyas, Vaishyas) enjoyed religious rights, while Shudras and women were excluded from Vedic studies and rituals.