The technique, which is fastest for measuring organic carbon is,

Correct option is D

Introduction
· Organic carbon measurement is a critical parameter in environmental monitoring used to assess the degree of pollution in water bodies and the efficiency of wastewater treatment processes.
· Different analytical techniques measure the oxygen required to stabilize organic matter or directly quantify the carbon atoms present in the sample.
· The choice of method depends on the required precision, the nature of the organic matter, and the time sensitivity of the monitoring task.

Information Booster
· TOC (Total Organic Carbon) is the fastest method because it utilizes high-temperature combustion or UV-persulfate oxidation to convert organic carbon into carbon dioxide ($CO_2$) within minutes.
· Unlike biological or chemical oxygen demand tests, TOC directly measures the carbon content using an infrared detector (NDIR), providing a result in typically 3 to 10 minutes.
· It is highly efficient for real-time monitoring and process control in industrial water treatment and high-purity water systems.
· The method is independent of the oxidation state of the organic matter and is not affected by the presence of inorganic reducing agents that often interfere with chemical tests.
· Modern TOC analyzers are fully automated, allowing for high sample throughput compared to traditional wet chemistry methods.

Additional Knowledge
· COD (Chemical Oxygen Demand) uses a strong chemical oxidizing agent (potassium dichromate) under acidic conditions to break down organic matter, usually taking about 2 to 3 hours to complete the reflux process.
· BOD5 (5-day Biochemical Oxygen Demand) is the standard biological test measuring the amount of dissolved oxygen consumed by microorganisms, but it is extremely slow as it requires a mandatory incubation period of 5 days.
· BOD7 refers to a 7-day variation of the biochemical oxygen demand test used in some European standards or specific research conditions, which makes it even slower than the standard 5-day protocol.
· While TOC is the fastest, it does not distinguish between biodegradable and non-biodegradable organic matter, which is why biological tests like BOD5 and BOD7 are still required to understand the ecological impact of waste on aquatic life.