To find out whether the water has been properly chlorinated, the test used is –
**Core Concept**
The question is testing the student's knowledge of water disinfection methods, specifically the test used to determine if water has been properly chlorinated. Chlorination is a widely used method for disinfecting water, and the test used to check its effectiveness is crucial for public health.
**Why the Correct Answer is Right**
The correct test used to determine if water has been properly chlorinated is the Orthotolidine (OT) test. This test measures the amount of free chlorine in water, which is essential for effective disinfection. Free chlorine is a strong disinfectant that kills bacteria, viruses, and other microorganisms. The OT test involves adding an orthotolidine solution to a water sample, which reacts with the free chlorine to produce a yellow-colored compound. The intensity of the color is directly proportional to the amount of free chlorine present. The test is widely used in water treatment plants and laboratories to ensure that water is properly disinfected.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the DPD (N,N-diethyl-p-phenylenediamine) test is used to measure the amount of chlorine in water, but it is not the primary test used to determine if water has been properly chlorinated.
**Option B:** This option is incorrect because the chlorine demand test is used to measure the amount of chlorine required to disinfect water, but it is not a test used to check the effectiveness of chlorination.
**Option C:** This option is incorrect because the total chlorine test is used to measure the amount of total chlorine in water, which includes both free and combined chlorine. While this test can provide some information about the chlorination process, it is not the primary test used to determine if water has been properly chlorinated.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the OT test is a qualitative test, meaning it provides a visual indication of the presence of free chlorine in water. The DPD test, on the other hand, is a quantitative test, providing a numerical value for the amount of chlorine present. Water treatment plants often use a combination of both tests to ensure proper chlorination.
**Correct Answer: C. Orthotolidine (OT) test.**