No, Mars is not the closest planet to the Sun. The planet that holds that title is Mercury.
Mercury orbits the Sun at an average distance of about 57.9 million kilometers (36 million miles), making it the innermost planet of our solar system. In contrast, Mars, which is the fourth planet from the Sun, orbits at an average distance of about 227.9 million kilometers (141.6 million miles).
This distinction is important because the proximity of planets to the Sun affects their climate, temperature, and atmosphere. Mercury, being so close to the Sun, experiences extreme temperature variations, while Mars has a colder and more variable climate.