Which one of the following rivers listed below is NOT a tributary of the river Ganga (Ganges) in the Indian river system?

Introduction / Context:
The Ganga (Ganges) river system is one of the major river systems of India, with numerous important tributaries contributing to its flow from the Himalayas and the plains. For geography and general knowledge exams, it is common to test whether a candidate can correctly identify which rivers belong to a particular system and which belong to others, such as the Brahmaputra system. This question asks you to select the river that is not a tributary of the Ganga from the given list.

Given Data / Assumptions:

• The main river in question is the Ganga (Ganges).
• The options are Son, Mahananda, Teesta and Sharada.
• We assume standard school level geography about Indian river systems.
• The task is to find the river associated instead with another major system, such as the Brahmaputra.

Concept / Approach:
The Son (or Sone) river originates in central India and joins the Ganga near Patna in Bihar, making it a major southern tributary of the Ganga. The Mahananda river, flowing through parts of Bihar and West Bengal, also joins the Ganga system. The Sharada (or Mahakali) river, arising in the Himalayas, eventually contributes to the Ganga system through its confluence with other tributaries. The Teesta river, however, originates in Sikkim, flows through West Bengal, and then enters Bangladesh to join the Brahmaputra (Jamuna) river, not the Ganga. Therefore, Teesta is correctly identified as not being a tributary of the Ganga.

Step-by-Step Solution:

Verification / Alternative check:
Standard maps of Indian river systems mark the Teesta as a major tributary of the Brahmaputra in Bangladesh. In contrast, maps of the Ganga basin highlight the Son, Mahananda and Sharada rivers as part of the Ganga system. Exam oriented summaries often include a list of important Ganga tributaries, in which Teesta is typically absent, while Son and Mahananda are present. This clear difference helps confirm that Teesta is the correct choice as the non Ganga tributary.

Why Other Options Are Wrong (they are Ganga tributaries):

• Son: A major right bank tributary of the Ganga, joining it near Patna in Bihar.
• Mahananda: An important tributary flowing through Bihar and West Bengal before merging with the Ganga system.
• Sharada: A Himalayan river that ultimately contributes to the Ganga basin and is treated as part of the Ganga river system.

Common Pitfalls:
Students sometimes confuse the Teesta river's course due to its presence in North Bengal and assume it must join the Ganga. Another pitfall is to think that any river in eastern India eventually connects to the Ganga. To avoid such mistakes, it is helpful to memorise a few key associations: Teesta with the Brahmaputra, and Son and Mahananda with the Ganga. Checking maps carefully during preparation further strengthens this understanding.

Final Answer:
The river that is not a tributary of the Ganga is the Teesta river.