The 'NISAR satellite' is jointly developed by which of the following organizations?

1. A

   ISRO and NASA

   ISRO and NASA. This option states that the NISAR satellite is a joint project between the Indian Space Research Organisation and the National Aeronautics and Space Administration of the United States. This partnership combines NASA's advanced radar imaging with ISRO's spacecraft bus and launch capabilities to measure Earth's changes with unprecedented detail, making it the correct official key for this question.

2. B

   ESA and ISRO

   ESA and ISRO. This choice claims the European Space Agency is a partner, which is incorrect because ESA is not involved in the NISAR mission.

3. C

   ESA and NASA

   ESA and NASA. This alternative incorrectly names the European Space Agency instead of the Indian Space Research Organisation alongside NASA.

4. D

   ROSCOSMOS and CNSA

   ROSCOSMOS and CNSA. This option incorrectly attributes the development of the NISAR satellite to the Russian and Chinese space agencies.

Summary. Official key is (a) ISRO and NASA. The question asks about the joint development of the NISAR satellite. Option (a) correctly identifies the collaboration between India's ISRO and America's NASA. Options (b), (c), and (d) incorrectly substitute other international space agencies such as ESA, ROSCOSMOS, or CNSA. Therefore, option (a) is the only valid choice.