p-Hydroxyazobenzene is also called as

Orange dye

The correct answer is option 3. Orange dye.

p-Hydroxyazobenzene is a compound belonging to the class of azo dyes. Azo dyes are characterized by the presence of one or more azo (-N=N-) groups in their molecular structure. These dyes are widely used in various industries, including textiles, cosmetics, and food, due to their vibrant colors and ease of synthesis.

The name "p-hydroxyazobenzene" gives us some clues about its molecular structure. The "p" indicates the position of the hydroxy (-OH) group on the benzene ring, which is in the para position (opposite to the azo group). The presence of the azo group (-N=N-) is implied by the term "azobenzene." This structure is represented as:

The p-hydroxyazobenzene molecule appears orange due to its absorption properties in the visible spectrum. It absorbs primarily in the blue and green regions of the spectrum, leaving the complementary color, which is orange, to be reflected and perceived by our eyes.

Now, let's discuss why p-hydroxyazobenzene is commonly referred to as an "Orange dye":

1. Color Appearance:  As mentioned earlier, p-hydroxyazobenzene reflects orange light due to its absorption properties in the blue and green regions. This characteristic makes it suitable for producing orange hues in various applications.

2. Application in Dyeing: p-Hydroxyazobenzene and its derivatives are extensively used in the textile industry to impart orange coloration to fabrics. By adjusting the molecular structure and substituents on the aromatic rings, the shade and intensity of the orange color can be controlled, allowing for a wide range of dyeing options.

3. Identification:  The term "Orange dye" serves as a convenient descriptor to identify and categorize dyes based on their predominant color. While p-hydroxyazobenzene may not be the only compound used to produce orange dyes, it is a significant contributor to the orange color spectrum in dyeing applications.

4. Historical Context: Over time, certain compounds become associated with specific colors due to their widespread use and recognition in various industries. p-Hydroxyazobenzene has likely earned its colloquial name "Orange dye" through historical usage and common association with orange-colored materials.

In summary, p-hydroxyazobenzene is commonly known as an "Orange dye" due to its molecular structure, absorption properties, applications in dyeing textiles, and historical context within the dye industry