Environmental health: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

PSM · Environmental health

Sample item

In the chlorination of water, what does the break-point signify?

AThe point of maximum formation of chloraminesBThe point at which chlorine demand begins to riseCThe point beyond which added chlorine appears as free residual chlorineDThe point at which all bacteria are killed regardless of contact time

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. The point beyond which added chlorine appears as free residual chlorine

As chlorine is added, it first reacts with reducing substances and then with ammonia to form chloramines, which peak just before the break-point. Beyond the break-point, the demand is satisfied and further chlorine appears as free residual chlorine.

Option by option

A. The point of maximum formation of chloramines
Combined chloramine concentration peaks before the break-point and then falls.
B. The point at which chlorine demand begins to rise
Chlorine demand is the amount consumed by the water before residual chlorine appears, and it does not begin at the break-point.
C. The point beyond which added chlorine appears as free residual chlorine (correct)
Correct. After the demand is met, added chlorine remains as free residual chlorine.
D. The point at which all bacteria are killed regardless of contact time
Disinfection depends on dose and contact time, so the break-point does not by itself guarantee killing of all bacteria.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, The point beyond which added chlorine appears as free residual chlorine. As chlorine is added, it first reacts with reducing substances and then with ammonia to form chloramines, which peak just before the break-point.

Why is "The point of maximum formation of chloramines" not the answer?

Combined chloramine concentration peaks before the break-point and then falls.

Why is "The point at which chlorine demand begins to rise" not the answer?

Chlorine demand is the amount consumed by the water before residual chlorine appears, and it does not begin at the break-point.

Why is "The point at which all bacteria are killed regardless of contact time" not the answer?

Disinfection depends on dose and contact time, so the break-point does not by itself guarantee killing of all bacteria.

What concept does this question test?

It tests Environmental health in PSM. Beyond the break-point, the demand is satisfied and further chlorine appears as free residual chlorine.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.