Explanation: The brightness of a planet in the night sky is determined by several factors, including its albedo (reflectivity), distance from the Sun, and distance from Earth. The albedo is a measure of how much light a planet reflects back into space. A higher albedo means more light is reflected, making the planet appear brighter.
Venus is the brightest planet in the solar system due to its high albedo, which is approximately 0.75. This high albedo is a result of the planet's thick cloud cover, which is composed primarily of sulfuric acid droplets. These clouds are highly reflective, bouncing a significant amount of sunlight back into space. Additionally, Venus is relatively close to Earth, which further enhances its visibility.
Mercury, the closest planet to the Sun, has a lower albedo of about 0.11. Despite its proximity to the Sun, Mercury's small size and lack of reflective atmosphere make it less visible from Earth compared to Venus. Mercury is often difficult to observe because it is frequently lost in the Sun's glare.
Earth, with an albedo of about 0.3, is not the brightest planet in the solar system. While it is the third planet from the Sun and has a moderate albedo, it is not as reflective as Venus. Earth's brightness is also not as noticeable from a distance because it is not covered in highly reflective clouds like Venus.
Mars, often called the "Red Planet" due to its reddish appearance, has an albedo of about 0.25. Mars is not the brightest planet in the solar system because it has a lower albedo than Venus and is farther from Earth, making it less visible.
In summary, Venus is the brightest planet in the solar system due to its high albedo and relatively close proximity to Earth, making it the correct answer to this question.