A single chlorine tablet of 0.5 grams is sufficient to disinfect ___________ liters of water.

Appeared in: UPPSC 2022

Explanation

A single 0.5-gram chlorine tablet is the standard recommended dose for disinfecting 20 liters of clear water.
This dosage is a widely accepted public health guideline for household water treatment, particularly in community and emergency settings.
The 20-liter volume corresponds to common household water storage containers like buckets or jerrycans, making the instruction easy to follow.
The tablet releases free chlorine, which acts as a powerful disinfectant against most waterborne bacteria and viruses after a sufficient contact time.

Option A: Using a 0.5g tablet for only 5 liters of water would result in significant over-chlorination. This would make the water taste and smell strongly of chlorine and is an inefficient use of the tablet.
Option B: Disinfecting only 7 liters with a 0.5g tablet is also incorrect and leads to over-chlorination and waste. It does not align with public health guidelines.
Option C: While closer to the correct volume, 15 liters is not the standard. Using the full tablet would lead to a slightly higher than necessary chlorine concentration.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Water purification dosage for chlorine tablets as background academic context rather than a clinical decision trigger.
Community health nurses must educate families on correct water purification methods to prevent waterborne diseases like cholera, typhoid, and diarrhea.
In disaster relief situations, providing chlorine tablets and clear instructions on their use (1 tablet per 20L bucket) is a critical first-line intervention to ensure safe drinking water.
What if? If the water is visibly cloudy or muddy (turbid), the nurse should instruct the user to first filter the water through a clean cloth. If filtration is not possible, the chlorine dose should be doubled (two 0.5g tablets for 20 liters) to overcome the organic load and ensure effective disinfection.

How to Approach the Question

Identify the question as a factual recall question about a standard public health measure.
Recognize the keywords: '0.5 grams chlorine tablet' and 'disinfect water'.
Recall the standard dosage used in community health and emergency preparedness for water purification.
Consider the practical application: chlorine tablets are often used with standard-sized water containers. A common size for a bucket or jerrycan is 20 liters.
Match this practical, standard volume to the dosage provided in the question.
Eliminate the other options as they do not correspond to the standard guidelines and would result in incorrect chlorine concentration.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 34-36

Practise the full UPPSC 2022

Attempt every question from this paper in a timed mock, then review the full solution for each one.