Which one is the most abundant of all the elements on Earth?

Oxygen is the most abundant element on Earth, both in the Earth's crust and as a major constituent of the planet as a whole. In the Earth's crust, oxygen is the most prevalent element, accounting for approximately 46.1% to 46.6% of its mass [1]. It is followed by silicon (about 27.7% to 28.2%) and aluminium (about 8.1% to 8.23%) [1]. When considering the entire Earth (including the core and mantle), iron is often cited as the most abundant by mass (34.6%), with oxygen following closely at 29.5% [1]. However, among the options provided (Silicon, Aluminium, Carbon, Oxygen), oxygen is consistently the most abundant across all geological reservoirs [1]. Carbon is relatively rare on Earth, making up less than 0.2% of the crust's mass. Therefore, oxygen is the correct choice as the most abundant element among the listed options.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > The Crust > p. 53