Identification: developing latent prints: practice question

A Forensic Medicine 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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Forensic Medicine · Identification: developing latent prints

Sample item

At a burglary scene, latent prints are suspected on a paper note and on a plastic carrier bag. Which pairing of method to surface is most appropriate?

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

The answer and the reasoning

B. Ninhydrin for the paper and cyanoacrylate fuming for the plastic

Ninhydrin reacts with amino acids absorbed into porous paper to give a purple product (Ruhemann's purple). Non-porous plastic holds the deposit on the surface, which is developed by cyanoacrylate (superglue) vapour that polymerises on the print. Choosing the method by the porosity of the surface is the rule.

Option by option

  • A. Ninhydrin for both surfaces

    Ninhydrin would not develop prints held only on the surface of non-porous plastic.

  • B. Ninhydrin for the paper and cyanoacrylate fuming for the plastic (correct)

    Correct. Ninhydrin suits porous paper and cyanoacrylate suits non-porous plastic.

  • C. Cyanoacrylate fuming for the paper and ninhydrin for the plastic

    This reverses the correct pairing; ninhydrin needs amino acids absorbed in porous material.

  • D. Iodine fuming for both surfaces

    Iodine fuming is a weaker, transient method and is not the best option for both.

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.

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Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is B, Ninhydrin for the paper and cyanoacrylate fuming for the plastic. Ninhydrin reacts with amino acids absorbed into porous paper to give a purple product (Ruhemann's purple).

Why is "Ninhydrin for both surfaces" not the answer?

Ninhydrin would not develop prints held only on the surface of non-porous plastic.

Why is "Cyanoacrylate fuming for the paper and ninhydrin for the plastic" not the answer?

This reverses the correct pairing; ninhydrin needs amino acids absorbed in porous material.

Why is "Iodine fuming for both surfaces" not the answer?

Iodine fuming is a weaker, transient method and is not the best option for both.

What concept does this question test?

It tests Identification: developing latent prints in Forensic Medicine. Non-porous plastic holds the deposit on the surface, which is developed by cyanoacrylate (superglue) vapour that polymerises on the print. Choosing the method by the porosity of the surface is the rule.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Identification: developing latent prints?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.