When a Bunsen burner is properly adjusted, which of the following best describes the appearance of its flame?

• A. The flame is orange and produces soot.
• B. The flame is yellow and flickering.
• C. The flame is completely invisible.
• D. The flame is blue with a distinct inner cone.

Answer: (D)

Verified step by step guidance

1. Understand that a Bunsen burner flame's appearance depends on the air-to-gas ratio, which affects combustion completeness.
2. Recognize that when the air hole is open, allowing sufficient oxygen to mix with the gas, the combustion is more complete, producing a blue flame.
3. Recall that a properly adjusted Bunsen burner flame has a blue color with a distinct inner cone, indicating efficient combustion and higher temperature.
4. Contrast this with an orange or yellow flame, which indicates incomplete combustion, producing soot and a cooler flame.
5. Conclude that the best description of a properly adjusted Bunsen burner flame is a blue flame with a distinct inner cone.