Which of the following planets may be suitable for the existence of life?

The correct answer is A. Mars is the only planet in this list where conditions may once have supported life, or may still support microbial life in protected niches.

• Mars (correct): It has evidence of ancient river valleys, lake beds and minerals that form in water, such as those studied in Jezero crater by NASA's Perseverance rover. Subsurface ice and a thin atmosphere mean conditions are harsh, but not ruled out for life.
• Mercury (wrong): It has almost no atmosphere, and its surface swings from about 430 degrees Celsius by day to about minus 180 degrees Celsius by night.
• Venus (wrong): A runaway greenhouse effect keeps its surface near 460 degrees Celsius, with crushing pressure and sulphuric acid clouds.
• Jupiter (wrong): It is a gas giant with no solid surface, dominated by hydrogen and helium. Its moon Europa is of interest for life, but Jupiter itself is not.

The core concept is the habitable zone, the range of distances from a star where liquid water can exist on a planet's surface. This links to Science and Technology and to Mains questions on space missions and the search for extraterrestrial life.

Trap: Many aspirants pick Venus because it is Earth's 'twin' in size and mass. Similarity in size does not make a planet habitable; surface temperature and atmosphere matter far more.