The instrument not typically used to determine the index of refraction of a volatile oil is:

The instrument not typically used to determine the index of refraction of a volatile oil is:

• A. Spectrophotometer
• B. Pycnometer
• C. Refractometer
• D. Polarimeter

Answer: (A)

Understanding how light bends in a liquid is key to measuring its index of refraction. A refractometer is designed for this purpose: it directly determines how much light speeds up or slows down as it enters the oil, giving a precise refractive index at a specific wavelength. A pycnometer, on the other hand, measures density by weighing a known volume, which tells you mass per volume but not how light travels through the liquid. A polarimeter assesses how the plane of polarized light rotates when passing through a chiral sample, providing optical rotation rather than refractive index. A spectrophotometer measures how much light is absorbed at different wavelengths to reveal concentration or identity, not the bending of light. Therefore, the instrument not typically used to determine the index of refraction is the spectrophotometer.