What is necessary in order for clouds to form when the atmosphere is absolutely stable? cooling of the air mass from below
a lifting mechanism other than convection (such as a front)
an environmental lapse rate less than 5°c
a high degree of subsidence

The correct option here is the first one.

Explanation:

Precipitation or humidity present in air or we can say the most air tends to rise above. And becomes colder and colder such that after a certain limit.  While the air can no longer take the weight of this water present in air bus resulting in condensation of water.

The pressure of colder air from below is necessary for cooler pushing it above, only this pressure by air can lead to formation of Clouds.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.