Oxygen is absent in?

Analysis

The question asks us to identify which of the listed substances does not contain oxygen in its chemical composition. We need to look at the chemical makeup of each option.

Concept Explanation

• Soil: Soil is a complex mixture containing minerals, organic matter, water, and air. Minerals in soil (like silicates and oxides) and water ($H_2O$) contain oxygen.
• Glass: Common glass (soda-lime glass) is primarily made of silica ($SiO_2$), along with sodium oxide ($Na_2O$) and calcium oxide ($CaO$). Oxygen is a major component here.
• Cement: Cement is typically made from limestone ($CaCO_3$), clay, and other minerals. These compounds are rich in oxygen (e.g., $CaO$, $SiO_2$, $Al_2O_3$).
• Kerosene: Kerosene is a mixture of hydrocarbons obtained from the fractional distillation of petroleum. Hydrocarbons consist exclusively of carbon and hydrogen atoms ($C_nH_{2n+2}$).

Step-by-Step Solution

1. Evaluate Soil: Soil contains water ($H_2O$) and various mineral oxides. Oxygen is present.
2. Evaluate Glass: Glass is composed of silica ($SiO_2$) and other metal oxides. Oxygen is present.
3. Evaluate Cement: Cement is composed of complex calcium silicates and aluminates, all of which contain oxygen. Oxygen is present.
4. Evaluate Kerosene: Kerosene is a hydrocarbon fuel. By definition, hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. There are no oxygen atoms in the molecular structure of pure kerosene.

Conclusion

Since kerosene is a hydrocarbon, it is the only substance among the options that lacks oxygen in its chemical structure.

Exam Tip: Whenever you see questions about the composition of fuels like petrol, diesel, or kerosene, remember they are hydrocarbons ($C_xH_y$). They are distinct from substances like carbohydrates or alcohols, which do contain oxygen.