The clouds float in the atmosphere because of their low

Clouds are masses of minute water droplets or ice crystals suspended at elevation [1]. They remain aloft primarily because the cloud as a whole is supported by the surrounding air: very small droplets (tens of micrometres) have extremely low terminal velocities and can be held up by gentle updrafts, so the droplet–air mixture behaves like a low–effective-density fluid compared with the denser surrounding air [2]. In buoyancy terms, if the average density of the cloud parcel (air plus droplets) is lower than the ambient air, there is a net upward force that keeps the cloud suspended; updrafts and small droplet size further reduce settling, so low density is the controlling factor.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Clouds > p. 333
2. [2] https://naturemuseum.org/cas/blog/how-do-clouds-float