In Indian physical geography, which of the following rivers is commonly regarded as the smallest river in India by length?

Introduction / Context:
Questions about the longest, largest, or smallest geographical features are common in general knowledge and competitive exams. In India, we frequently talk about long rivers such as the Ganga or the Godavari. However, this question tests your awareness of a much smaller river that is noteworthy for being considered one of the smallest rivers in India by length: the Arvari River in Rajasthan.

Given Data / Assumptions:

We are given:
- Names of major rivers like Indus, Godavari, Ganga, Narmada.
- One small river, Arvari, among the options.
- The question asks which is commonly regarded as the smallest river in India.

Concept / Approach:
The approach here is factual recall from Indian geography. While big rivers are famous for their length and basin size, some very short rivers gain attention for unique reasons such as conservation or local importance. The Arvari River in Rajasthan is often highlighted in environmental studies because it was revived from being seasonal to perennial through watershed management, and it is known for its very short length compared to other Indian rivers.

Step-by-Step Solution:
Step 1: Note that Indus, Godavari, Ganga, and Narmada are all long, well-known rivers.
Step 2: Recognize that Arvari is a relatively short river located in Rajasthan.
Step 3: Recall that Arvari is frequently mentioned in GK books and environmental case studies as the smallest river of India by length.
Step 4: Compare this with other options, which are clearly much longer rivers.
Step 5: Choose 'Arvari' as the correct answer.

Verification / Alternative check:
Standard GK sources and environmental case study materials describe Arvari as a small river, about a few tens of kilometres long, revived by community efforts in the Alwar district of Rajasthan. In contrast, the other rivers listed are hundreds or even thousands of kilometres long, making them clearly not the smallest.

Why Other Options Are Wrong:
- Indus: One of the longest rivers of Asia, flowing through multiple countries; not the smallest.
- Godavari: Known as the 'Dakshin Ganga', it is the longest river of peninsular India.
- Ganga: One of the major and longest rivers in India, sacred and geographically extensive.
- Narmada: A major river in central India, flowing through a long westward course into the Arabian Sea.

Common Pitfalls:
A common mistake is assuming the question might be a trick and choosing a familiar big river. Another is to confuse Arvari with a canal or local stream. Remember that even a short watercourse can be classified as a river, and GK questions often highlight such unique facts, especially where environmental restoration efforts are involved.

Final Answer:
Correct option: Arvari