17. Which element makes up the greatest % of the Earth's crust? a. potassium K b. sodium Na c. oxygen O d. hydrogen H e. silica

c. oxygen

Explanation:

Oxygen -

The most abundant element of the Earth's crust is the oxygen, which constitutes to 46.6 %.

Oxygen is mainly found in the combined form as, phosphates, carbonates.

It has many application in the field of medicine, industries and commercial purpose.

In hospital it is used for the treatment of respiratory diseases.

Hence, the most abundant element on planet earth is c. oxygen.