The reason for there being no atmosphere on the Moon is; option [D]. The escape velocity of gas molecules on it is less than their root mean square velocity. This means that gas molecules on the Moon can attain speeds greater than the escape velocity, allowing them to escape into space rather than remain bound by lunar gravity. As a result, the Moon lacks a significant atmosphere, unlike Earth, where the escape velocity is higher, allowing the atmosphere to be retained. Other factors such as proximity to Earth (option A), receiving sunlight (option B), and orbiting the Earth (option C) do not directly determine the presence or absence of an atmosphere on the Moon.