Correct option is B
The full form of N.P.L. in the context of the Gauge Interferometer is National Physics Laboratory. The National Physics Laboratory (NPL) is a renowned national metrology institute, where various standards of measurement are maintained. The NPL Gauge Interferometer is a precision instrument used in the field of metrology to measure distances or lengths with very high accuracy, based on the interference of light.
- Nikon Pulsed Laser and Nuclear Plasma Laboratory are unrelated to the context of gauge interferometry.
- Nuclear Physics Laboratory does not fit in the context of metrological equipment like the NPL Gauge Interferometer.
Thus, the correct answer is National Physics Laboratory.
