Combustible substance:
A combustible substance is a material that has the ability to burn or catch fire easily. It refers to substances that can undergo combustion, a chemical reaction that releases heat and light. Combustible substances are often used as fuels for various purposes, such as heating, cooking, and generating energy.

Permeable substance:
A permeable substance refers to a material or substance that allows the passage or flow of another substance, such as a liquid or gas, through its pores or spaces. Permeable substances can be used in filtration systems, where they allow the separation of different components based on their sizes or properties.

Non-combustible substance:
A non-combustible substance is a material that does not easily burn or catch fire. These substances have a high resistance to combustion and are not easily affected by heat or flames. Non-combustible materials are often used in construction and manufacturing to enhance safety and reduce the risk of fire accidents.

Impermeable substance:
An impermeable substance refers to a material or substance that does not allow the passage or flow of another substance through its pores or spaces. Impermeable substances are often used to create barriers or prevent the leakage of fluids or gases. They are commonly used in the construction of containers, pipes, and other structures that require containment or isolation.

Explanation:
The correct answer to the given question is option 'A' - Combustible substance. This is because substances that can burn easily are referred to as combustible substances. These materials have the ability to undergo combustion, releasing heat and light in the process. Combustible substances are used as fuels and can be ignited by a heat source or an open flame. Examples of combustible substances include wood, paper, gasoline, and natural gas.

It is important to understand the properties of different substances, particularly their flammability, to ensure safety in various situations. Combustible substances should be handled and stored with caution to prevent accidents and minimize the risk of fire.

Combustile substance