Within the World Bank Group, which institution is popularly known as the soft loan window because it provides very concessional loans and grants to the world poorest countries?

Introduction / Context:
The World Bank Group consists of several institutions that provide different types of financial assistance to countries. One of these institutions focuses on giving very low interest or interest free loans and grants to the poorest nations, with long repayment periods and generous terms. Because of these easy conditions, it is often called the soft loan window of the World Bank. This question asks you to identify that specific institution.

Given Data / Assumptions:
- The organisation in question is part of the World Bank Group.
- It is known as the soft loan window because it offers highly concessional finance.
- The options are IDBI, IDA, IMF, and RBI.
- We assume awareness of the main roles of each option.

Concept / Approach:
The International Development Association is the arm of the World Bank Group that provides soft loans and grants to the poorest countries. Its loans have very low or zero interest and long repayment periods. In contrast, the International Bank for Reconstruction and Development lends on near market terms. IDBI and RBI are Indian institutions, not part of the World Bank Group, and the IMF is a separate international organisation. Recognising IDA role allows us to answer correctly.

Step-by-Step Solution:
Step 1: Identify which of the options belongs to the World Bank Group. Step 2: Note that International Development Association, or IDA, is one of the five main institutions of the World Bank Group. Step 3: Recall that IDA provides concessional loans and grants to low income countries with long maturities and low charges. Step 4: Understand that this role is described as the soft loan window function. Step 5: Choose International Development Association (IDA) as the correct answer.

Verification / Alternative Check:
Economic and international organisation notes commonly describe IDA as the soft loan window of the World Bank. They contrast it with IBRD, which lends on harder terms. No such description is applied to IMF, IDBI, or RBI. The IMF does have some concessional facilities, but it is not part of the World Bank Group and is not labelled the soft loan window of the World Bank. This cross check confirms IDA as correct.

Why Other Options Are Wrong:
Industrial Development Bank of India (IDBI): This is an Indian financial institution and not a member of the World Bank Group, so it cannot be the soft loan window of the World Bank.
International Monetary Fund (IMF): A separate global organisation focusing on monetary stability and balance of payments support, not described as the soft loan window of the World Bank.
Reserve Bank of India (RBI): India central bank which manages monetary policy and banking regulation within India, again not part of the World Bank Group.

Common Pitfalls:
Some learners may confuse IDA with IMF or think that any institution offering concessional terms automatically fits the soft loan window label. Another error is to overlook that the question is about an institution within the World Bank Group, which rules out IDBI and RBI. Keeping clear mental maps of which organisations belong to which group helps avoid these mistakes.

Final Answer:
The institution known as the soft loan window of the World Bank is the International Development Association (IDA).