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.

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PSM · Environmental health

Sample item

After one hour of contact time, what residual free chlorine level is generally recommended in disinfected drinking water?

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

The answer and the reasoning

B. 0.5 mg/L

A free residual chlorine of about 0.5 mg/L after one hour of contact is the commonly taught standard. It ensures protection against recontamination in the distribution system.

Option by option

  • A. 0.05 mg/L

    0.05 mg/L is too low to protect.

  • B. 0.5 mg/L (correct)

    Correct.

  • C. 5 mg/L

    5 mg/L would taste strongly of chlorine and is unnecessarily high.

  • D. 50 mg/L

    50 mg/L is far above acceptable levels.

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.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, 0.5 mg/L. A free residual chlorine of about 0.

Why is "0.05 mg/L" not the answer?

0.05 mg/L is too low to protect.

Why is "5 mg/L" not the answer?

5 mg/L would taste strongly of chlorine and is unnecessarily high.

Why is "50 mg/L" not the answer?

50 mg/L is far above acceptable levels.

What concept does this question test?

It tests Environmental health in PSM. 5 mg/L after one hour of contact is the commonly taught standard. It ensures protection against recontamination in the distribution system.

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.