The material generally used for soundproofing of rooms like a recording studio and auditorium is:
a. cotton
b. coir
c. wood
d. Styrofoam
Styrofoam is typically used for sound-sealing spaces that absorb sound and promote sound sealing, such as assembly halls, cinema lobby areas and chronicle studios. Earplugs are made of cottonwood or fine glass wool that has been saturated with wax, whilst ear coverings have plastic foam or liquid sealing for captivating sound. Hence, (d) is the correct option.