* Hydrometers: These measure the specific gravity (density) of a liquid. In the context of water, specific gravity is closely related to salinity. Higher salinity means higher density.

* Salinometers: These are specifically designed to measure salinity, often using electrical conductivity as a proxy for salt content.

* Refractometers: These measure the refractive index of a liquid, which is also affected by salinity.

The other options are not measured by these instruments:

* pH: Measured by pH meters.

* Turbidity: Measured by turbidimeters or nephelometers.

* Dissolved oxygen: Measured by dissolved oxygen meters.