Which of the following is not a unitless constant?Choose answer: Reflactive index Relative density Gravitational constant Relative error

To determine which of the given options is not a unitless constant, we can analyze each option:

1. Refractive Index: This is a unitless quantity representing the ratio of the speed of light in a vacuum to the speed of light in a medium. It does not have units.

2. Relative Density (Specific Gravity): This is also unitless, as it is defined as the ratio of the density of a substance to the density of a reference substance (usually water for liquids).

3. Gravitational Constant (G): This constant is not unitless. It has units of $\text{m}^3 \text{kg}^{-1} \text{s}^{-2}$ (cubic meters per kilogram per second squared).

4. Relative Error: This is a measure of the uncertainty of a measurement compared to the size of the measurement itself and is also unitless, as it is a ratio.

Conclusion

The option that is not a unitless constant is the Gravitational Constant.