The correct descending order of the countries by population is option 3: Indonesia, Brazil, Russia, Japan.

Starting with Indonesia, it is the 4th most populated country in the world making it the most populated among these four. Following Indonesia is Brazil, which is the 6th most populated country in the world.

Russia is next, with the 9th largest population in the world. Lastly, Japan is the 11th most populated country in the world.

Option 1 is incorrect as it places Brazil before Indonesia and Russia before Japan. Option 2 places Indonesia first, which is correct, but it then wrongly orders Japan, Brazil, and Russia. Option 4 is also incorrect, as it places Brazil first and Russia before Japan.