Heating of alkanes with fuming sulphuric acid or oleum at high temperature, which forms sulphonic acid, is called:(A) nitration(B) halogenation(C) sulphonation(D) oxidation

The process you're describing involves the reaction of alkanes with fuming sulfuric acid or oleum (a mixture of sulfur trioxide and sulfuric acid) to form sulfonic acids. This specific reaction is known as **sulphonation**.

Here's a brief explanation of each option:

- **(A) Nitration**: This involves the introduction of a nitro group (-NO₂) into an organic compound, usually through the reaction of the compound with a mixture of nitric acid and sulfuric acid.

- **(B) Halogenation**: This refers to the introduction of halogen atoms (like chlorine or bromine) into an organic compound, typically through a reaction with a halogen (e.g., Cl₂ or Br₂) in the presence of heat or light.

- **(C) Sulphonation**: This is the process you described. When alkanes react with fuming sulfuric acid or oleum, they form sulfonic acids (-SO₃H), which are important intermediates in organic synthesis.

- **(D) Oxidation**: This generally involves the addition of oxygen or the removal of hydrogen from a compound. It doesn't specifically refer to the formation of sulfonic acids.

Thus, the correct answer is **(C) sulphonation**.