The correct option is Water.
Explanation
The speed of light in a transparent medium is determined by its optical density, which is measured by the refractive index ($n$). The speed of light ($v$) in a medium is inversely proportional to its refractive index, governed by the relation $v = \frac{c}{n}$, where $c$ is the speed of light in a vacuum.
Comparative Analysis:
- To determine where light travels fastest, one must compare the refractive indices of the given media:
- Water: Refractive index $\approx 1.33$
- Kerosene: Refractive index $\approx 1.44$
- Turpentine oil: Refractive index $\approx 1.47$
- Since $v \propto \frac{1}{n}$, the medium with the lowest refractive index will support the highest speed of light.
- Among the options provided, water has the lowest refractive index (1.33). Therefore, light travels faster in water than in kerosene or turpentine oil.
Key Takeaway: Light travels fastest in the optically rarest medium (lowest refractive index). A higher refractive index implies a lower speed of light in that medium.