The correct answer is option 1: 1 only.

The International Solar Alliance (ISA) was indeed launched at the United Nations Climate Change Conference in 2015, which was also known as COP21 or the Paris Climate Conference. The ISA is an intergovernmental organization that aims to promote the use of solar energy in the 121 countries between the Tropics of Cancer and Capricorn.

However, the second statement that the Alliance includes all the member countries of the United Nations is incorrect. As of September 2021, the ISA has 76 member countries, including India, France, Australia, and Brazil, among others. Notably, not all United Nations member countries have joined the ISA.

It is worth noting that the ISA has a unique membership structure in that it is open to all countries that lie within the Tropics of Cancer and Capricorn, regardless of their development status or economic situation. The ISA`s focus is on supporting developing countries in their efforts to adopt solar energy and reduce their dependence on fossil fuels.

In conclusion, only statement 1 is correct, and statement 2 is incorrect. The ISA was launched at the United Nations Climate Change Conference in 2015, but it does not include all the member countries of the United Nations.