Final answer:
Inhaling sulfur hexafluoride results in a lower pitch of voice because the gas is denser than air, slowing down sound waves. Humans normally change pitch by adjusting the tension on their vocal cords. The pitch change due to inhaling different gases is related to changes in sound wave properties. The correct option is b).
Step-by-step explanation:
Inhaling sulfur hexafluoride will make the pitch of one's voice lower. This is because sulfur hexafluoride is a gas that is much denser than air, which means the speed of sound is slower in sulfur hexafluoride compared to air.
The vocal cords vibrate at the same frequency, but because sound waves travel slower in sulfur hexafluoride, the wavelength of the sound emitted is longer which results in a lower pitch.
When humans change the pitch of their voice, they do so by relaxing or tightening their glottis, which affects the tension on the vocal cords and subsequently the frequency of the vibration, leading to different pitches.
The pitch of a sound from a moving source, such as a plane or a car, increases when the source is moving towards an observer and decreases when it moves away - this is known as the Doppler effect.
Overall, replacing the air in the lungs with a different gas like sulfur hexafluoride or helium changes the properties of the sound waves produced, leading to a noticeable change in the pitch of the voice. Option b) is the correct one.