This "answer" does not answer the "question" (which asks about elements, not compounds such as CO2, and has nothing to do with the shape of the Earth's magnetic field!) The fact that an element (such as Oxygen) is "locked away" in compunds (such as oxides) has nothing to do with the abundance of elements -- which was the point of the actual question.
It is correct to say that the answer depends somewhat upon "the chemical composition of the earth[']s core" but there is ample evidence to support the assumption that it is composed primary of iron (plus some nickel), and that leads to the correct answer that Iron is the most common element. Speculations about Titanium are unsupported, and do not add anything relevant to the answer to the question that was asked.
Carbon
One is silicon, but I don't know the other:(oxygen
Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium are the most common elements found in Earth's continental crust.
The most common element in the earth's crust is oxygen.
Helium is not one of the 8 most common elements in Earth's continental crust. The 8 most common elements are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Helium is a noble gas and is not as abundant in Earth's crust compared to these elements.
Carbon bonds with chlorine potassium and other solids and liquids to make salts.
The three most common elements of life are carbon, hydrogen, and oxygen. These elements are essential components of biological molecules like carbohydrates, lipids, nucleic acids, and proteins that make up living organisms.
These elements are nitrogen, oxygen and argon.
Carbon
The three most abundant elements in the Earth's atmosphere and the percents are:nitrogen-78,084 %, oxygen-20,946 % and argon-0,934 %.?
Hydrogen is the most common element in the universe. Helium, Oxygen, silicon, and aluminum are the next most common elements in the universe and on earth.
Oxygen and silicon are the two most abundant elements found in the most common minerals. The most common minerals found on Earth are silicates.
The three elements that make up most of Earth's mantle are oxygen, silicon, and magnesium.
One is silicon, but I don't know the other:(oxygen
Dirt and Dirt!
Carbon
Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium are the most common elements found in Earth's continental crust.