The earth's crust consists of different kinds of metals and non-metals. Humans have learned ways to harness each one of them for their uses. The most abundant non-metal element in the earth’s curst is Oxygen, and the most abundant metal element in earth's crust is aluminium.

Carbon is a non-metal which is most abundant in the earth crust not in free state but is in combined state.

The most abundant non-metal in the Earth's crust is Oxygen.

Oxygen is the most abundant non-metal element in the Earth's crust, accounting for approximately 46.6% of its mass. It is a vital element for life as we know it and plays a crucial role in many chemical processes. Here is a detailed explanation of why oxygen is the most abundant non-metal in the Earth's crust.

Abundance of Oxygen
- Oxygen is widely distributed in the Earth's crust, mainly in the form of oxides. It combines with various metals to form minerals, rocks, and soils. This abundance can be attributed to the high reactivity of oxygen, allowing it to readily form chemical bonds with other elements.
- The most common oxide in the Earth's crust is silicon dioxide (SiO2), also known as quartz. This mineral is composed of silicon and oxygen atoms, with oxygen accounting for about 53% of its mass.
- Oxygen is also present in other minerals like aluminum oxide (Al2O3), iron oxide (Fe2O3), and calcium carbonate (CaCO3), among others. These compounds contribute to the overall abundance of oxygen in the crust.

Role of Oxygen
- Oxygen is essential for the process of respiration in most living organisms, including humans. It is involved in the production of energy through cellular respiration, where oxygen molecules react with glucose to release energy in the form of ATP.
- Moreover, oxygen is crucial for the process of combustion, which is the rapid chemical combination of a fuel with oxygen. Combustion releases energy in the form of heat and light, making it an essential process for various human activities such as heating, cooking, and transportation.
- In addition, oxygen plays a significant role in the formation of ozone (O3) in the Earth's atmosphere. Ozone absorbs a significant portion of the Sun's harmful ultraviolet (UV) radiation, protecting life on Earth from its harmful effects.

Conclusion
In conclusion, oxygen is the most abundant non-metal element in the Earth's crust due to its high reactivity and widespread occurrence in the form of oxides. Its vital role in respiration, combustion, and ozone formation further highlights its significance in sustaining life on Earth.