In terms of atmospheric refraction, we can distinguish between cold and hot air. Which of the following statements is not true?

The statement "Hot air is denser than cold air" is the wrong one. 

Hot air is less dense than cold air because the mass of the air has not changed while the volume has increased. 

Warm air is lighter than cold air because it expands and takes up more space when heated. When something takes up more space, it becomes lighter and smaller. Because warm air is lighter, it rises. It has a slightly lower refractive index than cool air. Because the refracting medium's physical conditions (air) are not stationary, the object's apparent position appears to fluctuate when viewed through hot air. The wavering is caused by atmospheric refraction.

 Refraction occurs when a substance's refractive index changes. As a result, atmospheric refraction occurs in a medium with a changing refractive index.