Light speed in water is 2.25 times 10^5 m/s so the index of refraction is higher than the index of refraction of light in a vacuum which is 1.0. (speed in vacuum for light is 300,000 km/s)
Index of refraction of light in water is 3.0 time 10^5 m/s divided by 2.25 times 10^5 m/s = 1.33.
Hope this is what you wanted.
The vinegar is a charged molecule, whereas, the oil is neutral. As like dissolves like, the vinegar can be dissolved with charged molecules and the oil can be dissolved with neutrals. So, to mix vinegar and oil shaking is required.
In case, the person does not mix oil and vinegar dressing before pouring this on the salad, it would not produce a good taste, as the content of vinegar and the oil would not be appropriate.