Correct Answer:
B. Earth
Earth is the only planet in our solar system where free oxygen (O2) is abundantly available in the atmosphere. This is primarily due to the process of photosynthesis carried out by plants and algae over billions of years, which releases oxygen as a byproduct.
- Mars has a very thin atmosphere composed mostly of carbon dioxide, with only trace amounts of oxygen.
- Jupiter is a gas giant with an atmosphere primarily of hydrogen and helium, lacking free oxygen.
- Venus has a dense atmosphere dominated by carbon dioxide, with virtually no free oxygen.
The presence of free oxygen is a key indicator of life as we know it.