International Solar Alliance (ISA) is the alliance of countries most of which lie partially or completely

The correct option is Between tropic of cancer and tropic of capricorn.

The International Solar Alliance (ISA) is a collaborative platform designed to facilitate the rapid and massive deployment of solar energy. The alliance's geographical focus is directly related to the availability of solar resources across the globe.

Here is the step-by-step breakdown of why this is the correct answer:
1. The Tropics and Sunshine: The region of the Earth located between the Tropic of Cancer (approximately 23.5° North) and the Tropic of Capricorn (approximately 23.5° South) receives the most direct and intense sunlight throughout the year. The sun passes directly overhead at least once a year in these latitudes, ensuring high solar irradiance.
2. "Sunshine Countries": Because of this geographic alignment, the countries located within this tropical belt are often referred to as "Sunshine Countries" (or Suryaputras). They possess the highest potential for solar power generation but often face challenges in infrastructure, financing, and technology to harness it.
3. Founding and Purpose of ISA: The initiative was launched jointly by India and France at the COP21 Climate Conference in Paris in 2015. The core objective of the alliance is to bring these solar-rich countries together to aggregate demand, reduce the cost of solar technology, and mobilize investments to deploy solar energy projects effectively.