Activated charcoal is prepared by:
A. Adding \[B{a_3}{\left( {P{O_4}} \right)_2}\] to charcoal
B. Treatment with conc. $HN{O_3}$
C. Heating charcoal with steam to make it more porous
D. Adding silica to charcoal

Hint: When any organic material is heated either in absence of air or in very limited presence of air / oxygen, then the product which we get as residue is termed as charcoal. It is the impure form of graphitic carbon.

Complete Step by step answer: Activated charcoal is another form of carbon which has smaller, less volume pores which will increase the surface area. This availability of surface area falls in adsorption.
Charcoal is prepared by heating carbon containing materials (adsorption. shells, or sawdust) to a very high temperature. When they will be heated at a high temperature then the bonding sites which are in between layers get freed up. Due to which the size of pores present in the charcoal gets activated and makes more and more holes in the molecule which finally results in the increment of overall surface area.
It is quite amazing that only one teaspoon full activated charcoal contains more surface area than a football field.

Hence, option (C) heating charcoal with steam to make it more porous, is the correct option.

Note: Activated charcoal has a wide range of applications in various processes. It is used to store methane and hydrogen gas. It is also used as air purification. It is used in gold purification, used for extraction of metals, and used in treatment of sewage. It is also used in manufacture of hydrogen chloride.