Question

one of the greatest practical challenges faced by the international space station (iss) is the human need for oxygen. at first, the iss dealt with this by importing huge amounts of water from the earth, which was split by electric current into oxygen and hydrogen, the latter of which was ejected as waste. this system worked, but at an unsustainable cost of $300 million per refueling trip. a sustainable solution came in the form of the sabatier reaction, which fuses leftover hydrogen with the co2 that astronauts exhale to create water. this water can then be split into hydrogen and oxygen once more, creating an almost self - sustaining life support loop. which choice best states the main purpose of the text? a it describes a difficulty the iss faced in maintaining life support and the role of two different chemical reactions in addressing this challenge. b it summarizes the chemical reaction at the heart of the sabatier reaction, which has made life support on the iss more sustainable. c it explores a range of mutually incompatible approaches to life support that have been tried on the iss. d it argues that life support on the iss would be impossible without the reuse of chemical products through the sabatier reaction.

Explanation:

The text focuses on the challenge of providing oxygen for humans on the ISS, and how different chemical reactions (like the Sabatier reaction) are involved in attempts to create a self - sustaining life support system. It describes the difficulties faced in maintaining life support and the role of chemical reactions in addressing this challenge.

Answer:

A. It describes a difficulty the ISS faced in maintaining life support and the role of two different chemical reactions in addressing this challenge.