What class of fire involves the burning of wood, paper, cardboard, fabrics, and other similar materials?

"Class A"

Explanation:

Fire classes

According to the characteristics of combustion, different types of fires are determined, which we can group as follows:

1st Class A Fire

2nd Class B Fire

3rd Class C Fire

4th Class D Fire

Class "A": These are fires that involve solid organic materials, in which they can be formed, embers, for example, wood, paper, cardboard, straws, coals and textiles.

It has been standardized as a symbology to use a green background triangle inside which the letter A is placed.

Class "B": They are fires that involve flammable liquids and solids easily meltable by the action of heat (liquefiable solids). Within this area we can find all hydrocarbons, alcohols, paraffin, wax, etc.

It has been standardized as a symbology to use a red square inside the letter B.

Class "C": These are fires that involve energized electrical equipment, such as household appliances, switches, fuse boxes and power tools, etc.

It is symbolized with a blue background circle inside which the letter C is placed.

Class "D": They are flaring fires, in alkali and alkaline earth metals, as well as metal powders; they violently combustion and generally with a very intense flame, emit a strong caloric radiation and develop very high temperatures.

Water should NOT be used on this type of fires, as it would react violently. Within this type of fires are magnesium, sodium, potassium, titanium, zirconium, aluminum powder, etc.

It is symbolized with a five-pointed star with a yellow background inside the letter D.

K class :  Following a great difficulty in extinguishing fires in industrial fryers, this particular classification was made for this type of fires. It was then called Fuego K (by the initial of the English word Kitchen which means kitchen).

the answer is c.the valence of the atoms combine .