UPSC CAPF Archives

31. An electron and a photon have same de Broglie wavelength. It implies t

An electron and a photon have same de Broglie wavelength. It implies that they have the same

linear momentum

energy

speed

angular momentum

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UPSC CAPF – 2020

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If an electron and a photon have the same de Broglie wavelength (λ), it implies that they have the same linear momentum.

The de Broglie wavelength is given by the formula λ = h/p, where h is Planck’s constant and p is the linear momentum. If λ is the same and h is constant, then p must be the same.

While their momentum is the same, their energy and speed are generally different. For a photon, energy E = pc and speed is c. For an electron with mass m and speed v, momentum p = mv (non-relativistic) and kinetic energy KE = p^2/(2m). Same momentum p does not mean same energy or speed due to the difference in their mass and the relativistic nature of the photon.

32. Which one of the following is the major function of platelets ?

Which one of the following is the major function of platelets ?

Clotting of blood

O$_2$ transport

Immunity

Phagocytosis

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The major function of platelets (thrombocytes) in the human blood is to stop bleeding by initiating the process of blood clotting (hemostasis).

Platelets aggregate at the site of injury and form a plug, and they release factors that promote the coagulation cascade, leading to the formation of a fibrin clot.

Oxygen transport is primarily the function of red blood cells (erythrocytes) containing hemoglobin. Immunity is the function of white blood cells (leukocytes). Phagocytosis is a process carried out by certain white blood cells (like macrophages and neutrophils) to engulf and remove pathogens and debris.

33. In human beings, certain chemicals which cross the synapse between ner

In human beings, certain chemicals which cross the synapse between nerve cells are released from

cell body of nerve cell

nucleus of nerve cell

nerve endings of nerve cell

axon of nerve cell

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Neurotransmitters, which are chemicals that transmit signals across a synapse between nerve cells, are released from the nerve endings (axon terminals) of the presynaptic neuron.

The synapse is the junction between two nerve cells. When an action potential reaches the axon terminal, it triggers the release of neurotransmitters stored in vesicles into the synaptic cleft, where they bind to receptors on the postsynaptic neuron.

The cell body contains the nucleus and organelles, the nucleus contains genetic material, and the axon is the long projection that conducts the action potential away from the cell body. The nerve endings are specialized structures at the end of the axon.

34. In human body, the hormone which is secreted into blood and which cont

In human body, the hormone which is secreted into blood and which controls the rate of heart beat is

Adrenaline

Thyroxine

Insulin

Testosterone

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Adrenaline (also known as epinephrine) is a hormone secreted by the adrenal glands that increases the rate and force of heart beats, among other effects.

Adrenaline is part of the body’s “fight or flight” response, preparing the body for physical exertion by increasing cardiovascular activity.

Thyroxine regulates metabolism. Insulin regulates blood sugar levels. Testosterone is a primary male sex hormone involved in development and reproduction.

35. During respiration in human beings, the actual place of gaseous exchan

During respiration in human beings, the actual place of gaseous exchange is

Bronchi

Nasal passage

Alveoli

Trachea

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UPSC CAPF – 2020

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The actual place of gaseous exchange (oxygen and carbon dioxide) in the human respiratory system is the alveoli.

Alveoli are tiny air sacs in the lungs where the thin walls of the alveoli and surrounding capillaries allow for efficient diffusion of gases between the air and the blood.

Bronchi and trachea are airways that conduct air to and from the lungs but are not primarily sites of gas exchange. The nasal passage is involved in filtering, warming, and humidifying inhaled air.

36. In which of the following phylum, would you place an animal with a bil

In which of the following phylum, would you place an animal with a bilaterally symmetrical, triploblastic body without a true internal cavity (coelom) ?

Porifera

Platyhelminthes

Cnidaria

Annelida

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An animal with a bilaterally symmetrical, triploblastic body without a true internal cavity (coelom) would be placed in the phylum Platyhelminthes.

Phylum Platyhelminthes (flatworms) are characterized by bilateral symmetry and being triploblastic (having three germ layers: ectoderm, mesoderm, and endoderm). They lack a true coelom, meaning they are acoelomate – the space between the body wall and the digestive tract is filled with mesodermal tissue.

A) Porifera are asymmetrical or radially symmetrical, and diploblastic. C) Cnidaria are radially symmetrical and diploblastic. D) Annelida are bilaterally symmetrical and triploblastic, but they possess a true coelom (they are coelomates).

37. The eukaryotic chromatin is composed of

The eukaryotic chromatin is composed of

DNA only

DNA and Protein

DNA and RNA

RNA and Protein

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The eukaryotic chromatin is composed of DNA and Protein.

Chromatin is the complex assembly of DNA and proteins that packs DNA into a more compact structure. The primary proteins associated with DNA in chromatin are histones, around which the DNA double helix is wrapped like thread around spools. Non-histone proteins are also components of chromatin, playing roles in DNA replication, repair, transcription, and regulation.

While RNA molecules (like various non-coding RNAs and messenger RNA being transcribed) are often associated with chromatin, they are not considered a primary structural component in the same way as DNA and proteins (especially histones). The fundamental building block of chromatin is the nucleosome, which consists of DNA wrapped around a core of histone proteins.

38. Which one of the following is NOT a component of photochemical smog ?

Which one of the following is NOT a component of photochemical smog ?

Ozone

Peroxyacetyl nitrate

Polyaromatic hydrocarbons

Nitric oxide

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UPSC CAPF – 2020

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Polyaromatic hydrocarbons are NOT a direct component of photochemical smog formed by the reactions of NOx and VOCs.

Photochemical smog is primarily formed by the reaction of nitrogen oxides (NOx, primarily NO and NO2) and volatile organic compounds (VOCs) in the presence of sunlight. Key components produced by these reactions include ozone (O3), peroxyacetyl nitrates (PANs), aldehydes, ketones, and nitric acid. Nitric oxide (NO) is a precursor pollutant, quickly converted to NO2 which drives the photochemical process, so it is also present in the mixture. Polyaromatic hydrocarbons (PAHs) are complex organic compounds produced mainly from the incomplete combustion of organic matter (like in vehicle exhaust or burning wood). While PAHs are often present in polluted urban air (which experiences smog) and contribute to particulate matter, they are not formed *by* the photochemical reactions themselves.

Ozone (A) and Peroxyacetyl nitrate (B) are definitive, characteristic products and components of photochemical smog. Nitric oxide (D) is a primary pollutant and a crucial precursor (part of NOx) in the formation of photochemical smog.

39. Which one of the following methods can be used to remove permanent har

Which one of the following methods can be used to remove permanent hardness of water ?

Boiling

Ion-exchange

Lime treatment

Bubbling sulphur dioxide gas

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UPSC CAPF – 2020

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The Ion-exchange method can be used to remove permanent hardness of water.

Permanent hardness in water is caused by dissolved sulfates and chlorides of calcium and magnesium, which do not precipitate out upon boiling. The ion-exchange method, using materials like zeolite or synthetic resin, replaces the hard ions (Ca2+, Mg2+) with soft ions (usually Na+). This process is effective in removing both temporary and permanent hardness.

A) Boiling removes only temporary hardness (caused by bicarbonates). C) Lime treatment primarily removes temporary hardness by precipitating calcium and magnesium bicarbonates. Adding lime and soda ash (lime-soda process) can remove both. D) Bubbling sulfur dioxide gas through water forms sulfurous acid, which does not effectively remove the ions responsible for permanent hardness and is not a standard water softening method.

40. Which one of the following gases produces a red light when electricity

Which one of the following gases produces a red light when electricity flows through it ?

Helium

Argon

Nitrogen

Neon

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Neon gas produces a red light when electricity flows through it.

When an electric current passes through a low-pressure gas in a tube, the gas atoms are excited and emit light as they return to their ground state. Different gases emit light of characteristic wavelengths (colors). Neon gas specifically emits a bright reddish-orange light when used in discharge tubes, famously known as “neon signs.”

Helium typically emits a white, yellowish, or pinkish-orange light. Argon typically emits blue or violet light. Nitrogen can emit pink, orange, or yellow light depending on conditions. Other colors in commercial “neon signs” are often achieved by using different noble gases (like argon for blue) or by coating the inside of the tube with phosphors that fluoresce different colors when excited by the ultraviolet light emitted by gases like mercury vapor or argon.