Disposal of waste by landfilling is a common method used to manage and dispose of solid waste. However, it is important to note that while landfills are widely used, they are not without their drawbacks.

Landfilling as an Economical Method:
Landfilling is often considered an economical method of waste disposal because it requires relatively low upfront capital costs compared to other waste management options. It is a widely available and accessible option, making it a convenient choice for waste disposal.

Landfilling in Low Lying Areas:
Landfills are often preferred in low lying areas because the topography of such areas can make it more difficult to implement alternative waste management methods. The low-lying nature allows for easier excavation and construction of the landfill, reducing the overall cost and effort required.

Foul Gases Produced:
One of the major drawbacks of landfilling is the production of foul gases. When organic waste decomposes in a landfill, it produces a mixture of gases, including methane (CH4) and carbon dioxide (CO2). Methane is a potent greenhouse gas that contributes to climate change, while carbon dioxide is a major contributor to global warming. These gases can have negative environmental impacts if not properly managed and controlled.

Separation of Different Types of Waste:
In landfilling, there is generally no requirement for the separation of different types of waste. Unlike other waste management methods such as recycling or composting, where waste is sorted and processed based on its composition, landfills typically receive mixed waste. This lack of separation can lead to the accumulation of non-biodegradable and hazardous materials in the landfill, which can pose environmental and health risks.

The Correct Answer:
The correct answer for the question is option 'c' - "Foul gases are not produced." This is an incorrect statement. Landfills do produce foul gases, including methane and carbon dioxide, as mentioned earlier. Therefore, option 'c' is not correct regarding the disposal of waste by landfilling.