Acetylene, with the chemical formula C2H2, is considered a pure substance. Pure substances are characterized by having a fixed composition and distinct chemical properties. Acetylene perfectly fits this description as it consists of only two elements, carbon and hydrogen, combined in a constant 1:1 ratio by mole, forming a compound with very specific chemical and physical properties. Unlike mixtures, which are a physical combination of two or more substances, each retaining its own properties, the properties of acetylene are uniform and do not vary. Additionally, pure substances can be elements or compounds. Since acetylene is made up of more than one type of element chemically bonded together, it is classified as a compound, thus reinforcing its status as a pure substance.

Pigments in art refer to finely ground natural or synthetic materials that impart color to paints and other mediums. These substances absorb and reflect specific wavelengths of light, thus giving them their distinctive hues. Historically, pigments were derived from various sources, including minerals, plants, and insects. Artists carefully select pigments based on desired properties such as color strength, transparency, and durability. With technological advancements, synthetic pigments have expanded the color palette, offering vibrant and stable colors that were once unattainable. Pigments play a crucial role in artistic expression, allowing creators to convey emotions, depict realism, or explore abstract compositions. They are the heart of an artist's toolkit, emphasizing the importance of quality and selection in achieving the desired visual effect.

Yes, some people inject fish with dyes to enhance their color and make them more appealing to potential buyers. This practice is particularly common in the ornamental fish industry, where vibrant colors are highly sought after. However, it raises ethical and health concerns. Injecting dye is harmful to the fish and can significantly reduce their lifespan or cause health problems. Moreover, it can be deceptive to buyers who might believe they are purchasing a naturally colorful fish. Many aquarium enthusiasts and animal welfare advocates strongly oppose this practice, advocating for the appreciation of fish in their natural hues and promoting ethical breeding practices that can achieve bright colors without harm.