Which scientific phenomenon allows scientists to determine the chemical composition of stars?

• A. Thermal expansion
• B. Radioactive decay
• C. Electrolysis
• D. Emission spectrum

Answer: (D)

Verified step by step guidance

1. Understand that the question asks about the method scientists use to determine the chemical composition of stars.
2. Recall that each element emits light at specific wavelengths when excited, producing a unique pattern called an emission spectrum.
3. Recognize that by analyzing the light from stars through a spectroscope, scientists observe these emission lines to identify the elements present.
4. Note that thermal expansion, radioactive decay, and electrolysis are unrelated to identifying chemical composition in stars.
5. Conclude that the emission spectrum phenomenon is the key scientific principle enabling the determination of stellar chemical composition.