This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Unit of turbidity is calculated by ? 
Select and explain. 
A. Measuring the scattered light at 90deg, B. Measuring the scattered light at 180deg, C. Measuring the scattered light at 270deg, D. Measuring scattered light at 135deg
A: Measuring the scattered light at 90deg
Answer: A: Measuring the scattered light at 90deg 
Explanation: Ans: A. Measuring the scattered light at 90degIT is involved with measuring the amount of transmitted light (and calculating the absorbed light) by paicles in suspension to determine the concentration of the substance in question.Amount of absorbed light, and therefore, concentration is dependent on, Number of paicles, Size of paicleS, Measurements are made using light spectrophotometersTurbidity Unit is the International Standard Unit. Both measure the light scattered at 90o. NTU uses white light with peak spectral output at 400 to 680nm as light source. FTU uses Infrared monochromatic light with peak output at 780 to 900nm as light source.