Chlorine demand is measured by which of the following apparatus?
**Core Concept**
Chlorine demand refers to the amount of chlorine required to oxidize organic and inorganic matter in water, ensuring adequate disinfection. This concept is crucial in water treatment, as it determines the correct dosage of chlorine to achieve effective disinfection without excessive residual chlorine.
**Why the Correct Answer is Right**
The correct apparatus for measuring chlorine demand is a Chlorine Demand Apparatus, also known as a Chlorine Demand Test Kit. This apparatus typically consists of a series of glass tubes filled with water, each containing a different concentration of chlorine. The tubes are then placed in a darkened area and allowed to sit for a specified period, allowing the chlorine to react with the organic matter in the water. The tube that remains clear or least cloudy indicates the chlorine demand of the water. This apparatus measures the amount of chlorine required to oxidize the organic matter in the water, providing a crucial parameter for water treatment.
**Why Each Wrong Option is Incorrect**
* **Option A:** A Chlorine Demand Apparatus is not a type of pH meter, which measures the acidity or alkalinity of a solution.
* **Option B:** A DPD (N,N-diethyl-p-phenylenediamine) tube is used to measure residual chlorine in water, not chlorine demand.
* **Option C:** A chlorine demand apparatus is not a type of spectrophotometer, which measures the concentration of a solution by analyzing its absorbance of light.
**Clinical Pearl / High-Yield Fact**
Chlorine demand can be affected by various factors, including temperature, pH, and the presence of organic matter. It's essential to consider these factors when determining the correct chlorine dosage for water treatment.
**Correct Answer: D. Chlorine Demand Apparatus**