The lack of atmosphere around the Moon is primarily due to a combination of factors mentioned in option 1.

Option 1 states that the low escape velocity of air molecules and low gravitational attraction contribute to the absence of an atmosphere around the Moon.

Escape velocity is the minimum speed an object needs to reach in order to escape the gravitational pull of a celestial body. The Moon has a relatively low escape velocity, meaning that gas molecules on its surface can easily attain the required speed to escape into space.

Moreover, the Moon also has a weaker gravitational attraction compared to Earth. This lower gravity makes it harder for the Moon to hold onto any atmosphere that might have formed over time, as the weak gravitational pull cannot prevent the escape of gas molecules into space.

Option 2, high escape velocity of air molecule and low gravitational attraction, suggests that the high escape velocity alone is responsible for the lack of atmosphere. However, this overlooks the importance of the weak gravitational attraction of the Moon.

Therefore, the correct answer is option 1.