Most of the countries in International Solar Alliance lie

The correct answer is: Between tropic of cancer and Capricorn.

To understand why this is the correct answer, let us first understand what the International Solar Alliance (ISA) is and then connect it to geography.

What is the International Solar Alliance (ISA)?
The International Solar Alliance is a treaty-based intergovernmental organization jointly launched by India and France in 2015 at the Paris Climate Conference (COP21). Its primary objective is to promote the use of solar energy among its member countries to reduce dependence on fossil fuels and combat climate change.

Who are the member countries?
The ISA specifically targets countries that receive abundant sunlight throughout the year. According to its founding framework, ISA membership was originally open to countries that lie fully or partially between the Tropic of Cancer (23.5° N latitude) and the Tropic of Capricorn (23.5° S latitude). This tropical belt is known as the Sunshine Zone or the Solar Belt. Countries in this zone include nations from:

- South Asia: India, Sri Lanka, Bangladesh
- Southeast Asia: Thailand, Vietnam, Indonesia, Philippines
- Africa: Nigeria, Kenya, Ethiopia, Ghana, Senegal, Tanzania
- Latin America & Caribbean: Brazil, Colombia, Cuba, Mexico
- Pacific Island Nations: Fiji, Vanuatu, etc.

Why this belt specifically?
The region between the Tropic of Cancer and the Tropic of Capricorn is called the Tropics. This zone receives the most direct and intense solar radiation throughout the year because:

1. The Sun is directly overhead somewhere in this belt on every day of the year (between the solstices).
2. The angle of incidence of sunlight is very high, meaning more solar energy per unit area reaches the surface.
3. Days and nights are roughly equal and consistent, leading to a more predictable and abundant solar energy supply.

This makes these countries the most suitable and the most in need of harnessing solar power as a clean, renewable energy source.

Why the other options are incorrect:
- Above Tropic of Cancer: Countries in this zone (like Russia, Canada, northern Europe) lie in the temperate or polar regions where sunlight is seasonal and less intense — not ideal for solar energy focus.
- Below Tropic of Cancer: This is vague and only partially overlaps with the correct region; it does not accurately describe the ISA's target zone.
- In the Southern hemisphere: This is only half the picture. The ISA covers countries from both the Northern and Southern hemispheres, as long as they lie within the tropical belt.

Conclusion:
Since the ISA was founded to harness the abundant solar energy available in the tropical belt, most of its member countries naturally lie between the Tropic of Cancer and the Tropic of Capricorn — the region that receives maximum solar irradiance throughout the year. This is exactly why Option 3 is the correct answer.