In the Vedic literature, which one of the following Vedas is regarded as the earliest source that refers to the deity Rudra?

Introduction / Context:
The four Vedas are among the oldest sacred texts of Hindu tradition and contain hymns to various deities. Rudra, who is later identified with aspects of Shiva, appears in these early hymns. This question tests which Veda is considered the earliest textual source for references to Rudra.

Given Data / Assumptions:
- The focus is on Vedic literature, not on later epics or Puranas.
- The options list the four Vedas and an additional reference to later Puranas.
- We must identify the earliest Veda that refers to Rudra.

Concept / Approach:
The Rigveda is generally recognised as the oldest of the Vedas and contains numerous hymns dedicated to various deities, including Rudra. The other Vedas are derived in part from Rigvedic material and have more specialised ritual or musical roles. Therefore, if Rudra is present in the earliest Vedic hymns, the logical answer is the Rigveda. The approach is to recall the comparative age and content of the Vedas and link Rudra with Rigvedic hymns.

Step-by-Step Solution:
Step 1: Recall that the Rigveda is the earliest Veda and is mainly a collection of hymns.
Step 2: Remember that Rudra is mentioned in Rigvedic hymns as a powerful but somewhat fearsome deity associated with storms and healing.
Step 3: Recognise that the Samaveda largely consists of Rigvedic verses set to music, and the Yajurveda focuses on sacrificial formulas.
Step 4: The Atharvaveda contains spells and rituals but is not considered the first source for Rudra.
Step 5: Therefore, as the earliest Veda with hymns to Rudra is the Rigveda, option a is correct.

Verification / Alternative check:
Another way to check is to remember that when exam questions ask about the earliest mention of a deity, they often point back to the Rigveda since it is the oldest Vedic text. Later Puranas certainly elaborate on Shiva related theology but are clearly much later and cannot be the earliest source. Thus the combination of textual age and content supports Rigveda as the answer.

Why Other Options Are Wrong:
Option b is wrong because the Samaveda is derived from Rigvedic material and is concerned with musical chanting; it is not the primary earliest source.
Option c is wrong as the Yajurveda gives sacrificial formulas and is later in composition compared to Rigveda.
Option d is wrong because the Atharvaveda, while important, is again later and does not surpass the Rigveda in antiquity.
Option e is wrong since Puranas are part of later classical literature and therefore cannot be the earliest source.

Common Pitfalls:
A typical mistake is to think of Shiva and directly associate him with later Puranic literature, forgetting that Rudra is an earlier Vedic form. Some students also confuse which Veda is oldest. Memorising that Rigveda is the earliest and is mainly hymns helps quickly resolve such questions.

Final Answer:
The earliest Vedic source that refers to Rudra is the Rigveda.