Potassium and calcium are rarely found as pure elements in nature. They are usually combined with other substances. Explain why is this so.

Potassium and calcium are rarely found as pure elements in nature but are usually combined with other substances because of their high reactivity.

Reactivity of elements refers to the ability of atoms of elements to gain or lose electrons in order to form bonds with other elements.

The most reactive elements are those of group 1, 2 and 7.

Because of their reactivity, they do not occur free in nature but in combined forma with other elements. Example is potassium.

They are very reactive as well and lose their two valence electrons easily to forms ions. Because of their reactivity, they do not occur free in nature but in combined forma with other elements. Example is calcium.

Therefore, potassium and calcium are rarely found as pure elements in nature but are usually combined with other substances because of their high reactivity.

Learn more about reactivity of elements at: link

answer: the rate of diffusion increases with increase in temperature.

increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material.

generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.

b. is the answer hoped i