The correct answer from the given options is option 1, Earth. It is the largest planet in terms of its physical size. Earth is the third planet from the Sun and is part of the inner rocky planets known as terrestrial planets.

Option 2, Venus, is often referred to as Earth`s sister planet due to their similar size and composition. However, Venus is slightly smaller than Earth.

Option 3, Mars, is the fourth planet from the Sun and is smaller than both Earth and Venus. It is often called the "Red Planet" due to its reddish appearance.

Option 4, Mercury, is the closest planet to the Sun and is the smallest planet in our solar system. It is much smaller than Earth, making it the incorrect option.

In conclusion, Earth is the largest planet among the given options, making it the correct answer.