What Is the Most Abundant Element?

The most abundant element in the universe is hydrogen, which makes up about three-quarters of all matter! Helium makes up most of the remaining 25%. Oxygen is the third-most abundant element in the universe. All of the other elements are relatively rare.

The chemical composition of Earth is quite a bit different from that of the universe. The most abundant element in the Earth's crust is oxygen, making up 46.6% of Earth's mass. Silicon is the second most abundant element (27.7%), followed by aluminum (8.1%), iron (5.0%), calcium (3.6%), sodium (2.8%), potassium (2.6%). and magnesium (2.1%). These eight elements account for approximately 98.5% of the total mass of the Earth's crust. Of course, the Earth's crust is only the outer portion of the Earth. Future research will tell us about the composition of the mantle and core.

The most abundant element in the human body is oxygen, making up about 65% of the weight of each person. Carbon is the second-most abundant element, making up 18% of the body. Although you have more hydrogen atoms than any other type of element, the mass of a hydrogen atom is so much less than that of the other elements that its abundance comes in third at 10% by mass.

Source​

"Element Distribution in the Earth's Crust"