The correct option is 1.33.
Explanation
The refractive index ($n$) of a medium is a measure of the bending of a ray of light when passing from one medium into another. It is defined as the ratio of the velocity of light in a vacuum ($c$) to the velocity of light in the medium ($v$), expressed as $n = c/v$. A higher refractive index indicates a denser optical medium where light travels slower.
Analysis
The refractive index is a characteristic physical property of a substance. The standard approximate values for common media are:
- Vacuum: Exactly 1.
- Air: Approximately 1.0003 (often approximated as 1).
- Water: Approximately 1.33.
- Glass: Typically ranges from 1.5 to 1.9 depending on the composition (e.g., Crown glass is ~1.52, Flint glass is ~1.65).
Therefore, 1.33 is the correct approximate value for water.
Key Takeaway: The refractive index of water is 1.33, meaning light travels 1.33 times slower in water than in a vacuum. Common glass has a higher refractive index, typically around 1.5.