Your Answer : (Not Answered)

Correct Answer : C

The ratchet mechanism is associated with the revolver.

In a revolver the cylinder has a star-shaped ratchet at its rear. As the hammer is cocked or the trigger is pulled, a pawl (the hand) pushes against the ratchet and rotates the cylinder to bring the next chamber in line with the barrel, where the cylinder stop locks it.

Pistols feed from a magazine by slide action, shotguns by break, pump or semi-automatic action, and airguns by a spring or compressed gas, none of which uses a ratchet to index chambers.

Your Answer : (Not Answered)

Correct Answer : C

Assertion is false but Reason is true.

The maximum effective range of a bullet, the farthest distance at which it can still reliably cause the intended effect, is hard to state as a single figure. It depends on many things: bullet weight, velocity, diameter and construction, where the bullet strikes, and conditions such as wind and elevation. That is what the reason says.

Because so many factors are involved, the assertion that the range is 'often easy to quantify' is false, while the reason is true.

Your Answer : (Not Answered)

Correct Answer : C

The answer is (c) and (d) only: oxygen and silicon.

Oxygen and silicon have very small cross-sections for thermal neutron capture and give no useful activation products that way. With fast (14 MeV) neutrons, however, they undergo threshold reactions: \(^{16}\mathrm{O}(n,p)^{16}\mathrm{N}\) and \(^{28}\mathrm{Si}(n,p)^{28}\mathrm{Al}\), whose short-lived products are easily counted. Fast-neutron activation is therefore the standard way of determining oxygen and silicon.

Chlorine and nickel are measured more sensitively with thermal neutrons, through capture reactions such as \(^{37}\mathrm{Cl}(n,\gamma)^{38}\mathrm{Cl}\), so options including (a) or (b) are wrong.

Your Answer : (Not Answered)

Correct Answer : A

The glass is laminated glass.

Laminated glass is made of layers of glass bonded with plastic interlayers (polyvinyl butyral or polycarbonate). When struck, the glass cracks but the fragments stay attached to the interlayer, and several layers together can stop a bullet. Bullet-resistant screens are built this way, as are car windscreens.

Tempered glass is stronger than ordinary glass but shatters completely into small cubes, so it cannot stop a bullet. Crown glass is an old hand-blown window glass, and 'slit glass' is not a glass type.

Your Answer : (Not Answered)

Correct Answer : C

Pedologists are scientists who study soil.

Pedology (from the Greek pedon, soil or ground) is the study of soil in its natural setting: its formation, classification, layers and properties. Forensic soil examination draws on it to compare samples from a suspect's shoes or vehicle with a crime scene.

Glass, dyes and paint are studied by other specialists in trace evidence. The word should not be confused with paedology, the study of children.

Your Answer : (Not Answered)

Correct Answer : C

The body hair of the human foetus is non-medullated and non-pigmented.

Foetal body hair, called lanugo, is fine, soft and short. It has no medulla (central core) and little or no pigment, which makes it different from the coarser, pigmented terminal hair of adults. Its presence helps in estimating foetal age.

The single-feature options are incomplete, since lanugo lacks both a medulla and pigment, and 'medullated and pigmented' describes adult terminal hair.

Your Answer : (Not Answered)

Correct Answer : A

The method is differential extraction.

Sperm heads are protected by disulphide-rich protein, so they resist lysis. In differential extraction the swab is first digested with proteinase K and detergent without a reducing agent: the vaginal epithelial cells burst, and their DNA goes into the female fraction. The intact sperm are then spun down and lysed with dithiothreitol (DTT) added, giving a male fraction. This separates the victim's and the assailant's DNA.

Microwave-assisted, reflux and Soxhlet extraction are chemical extraction methods for organic compounds, not ways of separating cell types.

Your Answer : (Not Answered)

Correct Answer : C

The non-distilled alcoholic beverage is wine.

Wine is made by fermenting grape juice and is not distilled, so its alcohol content is limited by the yeast, usually to about 9 to 15 per cent.

Gin and rum are distilled spirits, made by distilling a fermented liquid to concentrate the alcohol. Sherry is a fortified wine: distilled grape spirit is added to it, which is why it is not the non-distilled beverage here.

Your Answer : (Not Answered)

Correct Answer : B

The 14 indicates the rim diameter.

In the tyre size P 195/75 R 14, P means a passenger-car tyre, 195 is the section width in millimetres, 75 is the aspect ratio (the sidewall height as a percentage of the width), R means radial construction, and 14 is the diameter of the wheel rim in inches.

The aspect ratio is 75 and the section width 195, so those options name the wrong numbers. Turning radius is a property of the vehicle, not of the tyre, and is not marked on the tyre at all.

Your Answer : (Not Answered)

Correct Answer : A

The objective of a medicolegal autopsy does not include identifying the accused.

A medicolegal autopsy is done to establish the identity of the deceased, the cause and manner of death, and the time since death, and to collect evidence. Its findings may later help investigators, but identifying the accused is the job of the police and the court, not of the autopsy.

The other three options are standard objectives listed in forensic medicine textbooks.

Your Answer : (Not Answered)

Correct Answer : A

The fastest shutter speed is 1/2000 second.

Shutter speed is the time the shutter stays open, so the smaller the fraction of a second, the faster it is. 1/2000 s is shorter than 1/1500, 1/1000 and 1/500 s, and is used to freeze fast movement.

The trap is to read the larger denominator as a longer time; in fact 1/500 s is four times longer than 1/2000 s.

Your Answer : (Not Answered)

Correct Answer : C

The keyed answer is freehand forgery.

A freehand forgery is written by a forger who has practised the genuine signature until it can be reproduced fluently, without tracing. A skilled freehand forgery lacks the tremor and slow, drawn strokes of a beginner's copy and keeps a natural rhythm, so it is the hardest kind to detect, and its detection relies on finer features such as proportions, pen lifts and habitual details.

Traced and lifted forgeries leave physical evidence, such as indentations, graphite or carbon guide lines and a slow, uniform line with no variation in pressure. A random forgery makes no attempt to copy the genuine form, so it is the easiest to detect.

Your Answer : (Not Answered)

Correct Answer : B

When a liquid is heated, its refractive index decreases.

Heating makes a liquid expand, so its density falls and there are fewer molecules per unit volume to slow the light. The refractive index therefore falls, by about 0.0004 to 0.0005 per degree Celsius for typical organic liquids.

This property is the basis of the glass refractive index measurement used in forensic glass comparison (the hot-stage method): a glass fragment is immersed in silicone oil, the oil is heated until its refractive index falls to match the glass, and the fragment's edges vanish at the match point.

Your Answer : (Not Answered)

Correct Answer : B

The correct matching is a-iii, b-iv, c-ii, d-i.

• Bhilawanol is the irritant principle of Semecarpus anacardium, the marking nut (iii).
• Hyoscyamine is an alkaloid of Atropa belladonna, deadly nightshade (iv).
• Nerin (oleandrin and neriodorin) is a cardiac glycoside of Nerium oleander, white oleander (ii).
• Calotoxin (printed 'Calatoxin') is a principle of Calotropis gigantea, madar (i).

Only the second code gives (iii), (iv), (ii), (i). These four plants are standard irritant and cardiac poisons in Indian toxicology.

Your Answer : (Not Answered)

Correct Answer : B

The transducer used in a mass spectrometer is the electron multiplier.

After ions are separated by their mass-to-charge ratio, they must be counted. In an electron multiplier, each ion striking the first dynode releases several secondary electrons, which are accelerated to the next dynode and multiplied again, giving a gain of about a million and a measurable current for even single ions. It is the standard detector in GC-MS and LC-MS instruments.

The electron capture detector is a gas chromatography detector for halogenated compounds, the bolometer is a thermal detector for infrared radiation, and the phototube detects light in UV-visible spectrophotometers.

Your Answer : (Not Answered)

Correct Answer : A

The key's answer is ethylene.

A vibration absorbs infrared radiation only if it changes the molecule's dipole moment. Hydrochloric acid and carbon monoxide are polar diatomic molecules whose single stretching vibration changes the dipole, so both absorb strongly in the IR, and nitric acid is a polar molecule with many IR bands.

Ethylene is a non-polar, centrosymmetric molecule. Its characteristic C=C stretching vibration is symmetric, causes no change in dipole moment, and is therefore IR inactive (it is seen in the Raman spectrum instead). Ethylene does have some other IR-active vibrations, but of the four it is the one whose key vibration is IR inactive, which is the reading the key takes.

Your Answer : (Not Answered)

Correct Answer : A

Criminal intent is mens rea.

Mens rea, 'guilty mind', is the mental element of a crime: intention, knowledge, recklessness or negligence, as the offence requires. Together with actus reus, the guilty act, it forms the basic structure of criminal liability, expressed in the maxim actus non facit reum nisi mens sit rea, the act does not make a person guilty unless the mind is also guilty.

Compos mentis (printed 'Compos men tis') means of sound mind, which bears on capacity rather than intent. Neurosis is a mental disorder and empathy is understanding another's feelings.

Your Answer : (Not Answered)

Correct Answer : B

The pitch pattern of a sentence is called intonation.

Intonation is the rise and fall of pitch across a phrase or sentence, which signals questions, statements, emphasis and emotion. In forensic speaker comparison, a speaker's habitual intonation patterns are among the features examined.

The fundamental frequency is the physical rate of vibration of the vocal folds at any one moment, which is heard as pitch; intonation is its pattern over the sentence. Timbre is voice quality, the property that makes two voices at the same pitch sound different, and phonology is the study of a language's sound system.

Your Answer : (Not Answered)

Correct Answer : A

The corrosiveness of gasoline is caused by sulfur.

Sulfur compounds left from crude oil, such as hydrogen sulphide, mercaptans and free sulfur, attack metals, especially copper and its alloys in fuel systems. The copper strip corrosion test measures this, and fuel standards limit sulfur content partly for this reason.

Water can cause rusting in tanks but is not a constituent responsible for the corrosiveness of the fuel itself, chloride is not a normal gasoline component, and lead (as tetraethyl lead) was an anti-knock additive.

Your Answer : (Not Answered)

Correct Answer : C

It is not called the migration time.

The time an unretained substance, travelling with the mobile phase, takes to pass through a chromatographic column from injector to detector is called the dead time, also the void time or hold-up time (written \(t_{M}\) or \(t_{0}\)). It is subtracted from retention times to give adjusted retention times.

Migration time is the term used in capillary electrophoresis for the time an analyte takes to reach the detector under the electric field. So dead time, void time and hold-up time are all names for the quantity, and migration time is not.