Which one of the following Indian States is included among the Seven Sisters of North Eastern India?

Introduction / Context:
The term Seven Sisters is a popular nickname for a group of contiguous states in North Eastern India. These states share similar geographical, cultural and historical features and are often discussed together in Indian geography and polity. Knowing which states belong to this group is a common requirement in competitive examinations. This question asks you to identify which given state is one of the Seven Sisters.

Given Data / Assumptions:
- The options include West Bengal, Odisha, Tripura, Bihar and Sikkim.
- The Seven Sisters traditionally refer to seven specific North Eastern states: Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura.
- Sikkim, although in the North Eastern Council, is usually described as the brother state and is not counted among the original Seven Sisters.
- We assume knowledge of basic political geography of India.

Concept / Approach:
The key to answering is recalling the exact list of Seven Sister states. These are Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura. They are contiguous and share borders with one another and with neighbouring countries. While Sikkim is also a North Eastern state and sometimes grouped with them for administrative purposes, it is not part of the original Seven Sisters grouping. States like West Bengal, Odisha and Bihar belong to eastern or central India, not to this special North Eastern cluster.

Step-by-Step Solution:
Step 1: Write out or mentally recall the Seven Sister states: Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura.Step 2: Compare this list with the options given in the question.Step 3: Notice that among the options, only Tripura appears in the standard list of Seven Sister states.Step 4: Recognise that West Bengal, Odisha and Bihar are eastern Indian states but not part of the Seven Sisters, and Sikkim is a separate North Eastern state often called the brother.Step 5: Select Tripura as the correct answer.

Verification / Alternative check:
As a check, you can look at a political map of North East India or refer to school geography textbooks, which explicitly label this group of states and often provide a brief explanation of the nickname Seven Sisters. These sources will consistently show Tripura included among the Seven Sisters while listing the others separately. This visual and textual confirmation strongly supports the selection of option C.

Why Other Options Are Wrong:
West Bengal, although it has a narrow corridor connecting mainland India to the North East, is not itself counted among the Seven Sisters, so option A is incorrect. Odisha lies on the eastern coast along the Bay of Bengal and is geographically distinct from the North Eastern states, making option B wrong. Bihar is an inland state in eastern India and not part of the North Eastern cluster, so option D is incorrect. Sikkim is a Himalayan state located between Nepal, Bhutan and West Bengal; while it is often grouped with the North Eastern region administratively, it is not part of the original Seven Sisters, so option E is not correct for this specific term.

Common Pitfalls:
Some learners mistakenly include Sikkim among the Seven Sisters because they know it is a North Eastern state and part of the North Eastern Council. Others confuse the term with a more general description of eastern India and may think states like West Bengal or Odisha are included. The safest approach is to memorise the precise list of seven states and to distinguish this from broader regional or administrative groupings.

Final Answer:
Tripura is the state among the given options that is included in the group popularly known as the Seven Sisters of North Eastern India.