D. None of the above.
The image shown is of a Hand held Refractometer
- It is a laboratory or field device for the measurement of an index of refraction (refractometry). .
- A traditional hand held refractometer is an analog instrument for measuring a liquid’s refractive index.
It works on the critical angle principle by which lenses and prisms project a shadow line onto a small glass reticle inside the instrument, which is then viewed by the user through a magnifying eyepiece.
There are many types of refractometers and the most common types are Abbe’s refractometer, Pulfrich refractometer, Immersion refractometer.