The coupling reaction between the diazonium salt of 4-amino benzene sulphonic acid and N, N-dimethyl benzamine produces Methyl orange.

Explanation:
- The diazonium salt of 4-amino benzene sulphonic acid is formed by the reaction between 4-amino benzene sulphonic acid and sodium nitrite in the presence of hydrochloric acid. This reaction is known as diazotization.
- The diazonium salt is highly reactive and can undergo coupling reactions with various compounds. In this case, it reacts with N, N-dimethyl benzamine to form Methyl orange.
- Methyl orange is an azo dye and is commonly used as an acid-base indicator. It is orange in acidic solutions and turns red in basic solutions.
- The reaction between the diazonium salt and N, N-dimethyl benzamine involves the formation of an azo compound. The diazonium group (-N2+) is replaced by the N, N-dimethyl benzamine moiety, resulting in the formation of Methyl orange.
- The reaction can be represented as follows:
diazonium salt of 4-amino benzene sulphonic acid + N, N-dimethyl benzamine → Methyl orange
- Methyl orange is widely used in analytical chemistry and is one of the most commonly used acid-base indicators. It is used to determine the pH of a solution by observing the color change.
- In acidic solutions, Methyl orange is protonated and exists in its orange form. In basic solutions, it loses a proton and exists in its red form.
- The color change of Methyl orange is due to the different electronic states of the azo group in acidic and basic environments. In an acidic solution, the azo group is in the more stable hydrazone form, resulting in an orange color. In a basic solution, the azo group is in the less stable azo form, resulting in a red color.
- Therefore, the correct answer is option C, Methyl orange.