Chemistry (Part-I) (UPSC)

Total Questions: 50

1. Which one of the following can be used to confirm whether drinking water contains a gamma emitting isotope or not? [1995]

Correct Answer: (c) Scintillation counter
Solution:Scintillation counter (scintillometer): An instrument which measures gamma radiation. It is also used in airborne and ground radiometre surveys. This instrument utilizes the flash of light emitted when the atoms of a suitable' phosphor' are energized by gamma rays. The scintillations are detected by a light sensitive cathode.

The flash of light which is produced by a transparent material due to the passage of a subatomic particle (electron, ion, alpha particle, or photon) is called scintillation. The scintillation counter is a device that is used to detect radiation by means of a scintillation effect. It is also known as a scintillation detector.

2. Which one of the following pairs of materials serves as electrodes in chargeable batteries commonly used in devices such as torchlights, electric shavers etc. [1995]

Correct Answer: (a) Nickel and cadmium
Solution:Nickel and cadmium are used as electrode in batteries. Nickel hydroxide as a positive and cadmium hydroxide is used as negative electrode in these batteries. The following chemical reaction takes place in the Nickel-cadmium batteries-
2NiO(OH) + Cd + 2H₂O ↔ 2Ni(OH), + Cd(OH)₂
Lithium-ion batteries are a type of rechargeable battery that stores energy by using a special process called intercalation. They are commonly used in portable electronic devices like cell phones and laptops, as well as electric cars. These batteries are known for their high energy density. This means they can store a lot of energy in a small and lightweight package. They are also more efficient and have a longer lifespan compared to other types of rechargeable batteries. In recent years, lithium-ion batteries have become increasingly popular due to their widespread use in various applications.

3. 'Yellow cake', an item of smuggling across border is : [1995]

Correct Answer: (c) uranium oxide
Solution:Yellowcakes are obtained through the milling and chemical processing of uranium ore, forming a coarse powder that has a pungent odor, is insoluble in water, and contains about 80% uranium oxide, which melts at approximately 2880 °C.

Uranium Element
• Uranium (U) is a radioactive chemical element of the actinide series of the periodic table, atomic number 92. Uranium is a dense, hard metallic element that is silvery white in colour. It is ductile, malleable, and capable of taking a high polish.
• Occurrence: Uranium occurs naturally in low concentrations in soil, rock and water and is commercially extracted from uranium-bearing minerals.
o Uranium occurs naturally in several minerals such as uraninite (pitchblende), brannerite and carnotite. It is also found in phosphate rock and monazite sands.
▪ Monazite sands occur on the east and west coasts and in some places in Bihar. But the largest concentration of monazite sand is on the Kerala coast.

4. The difference between a nuclear reactor and an atomic bomb is that : [1995]

Correct Answer: (b) the chain reaction in nuclear reactor is controlled
Solution:Nuclear fission is a perfect example of chain reaction. In case of nuclear fission a heavy atomic nucleus (such as that of uranium) disintegrates into two nearby equal fragments with release of large amount of energy when large number of nuclei are brought closer together. In such a case the neutrons released, when one nucleus splits, strikes other nuclei causing them to split and the process continues. Now atomic bomb and nuclear reactor both works on nuclear fission chain reaction but chain reaction in nuclear reactor is controlled by control rods, made up of metal cadmium or boron a neutron absorbing material, whereas in atomic bomb there is no neutron absorber. So chain reaction goes uncontrolled and is very violent.

5. The alpha particle carries two positive charge. Its mass is very nearly equal to that of: [1996]

Correct Answer: (b) an atom of helium
Solution:Each alpha particle contains two protons and two neutrons. Total number of nucleons Number of protons + Number of neutrons = 2+2=4 Total number of nucleons Mass number of an element Thus mass number of alpha particle is 4 which is equal to molecular weight of helium atom.
• Alpha particles primarily originate through the radioactive decay called alpha decay. In this process, heavy atomic nuclei (with atomic mass >106 u) emit an alpha particle, reducing their mass number by four. Alpha particles can also result from certain nuclear reactions in stars and constitute 10-12% of cosmic rays.
• The phenomenon of ternary fission, although rare, can produce especially energetic alpha particles, often called long-range alphas due to their higher energy compared to typical alpha decay particles.
Applications of Alpha Particles
• Used in cancer therapy, especially via techniques like Unsealed Source Radiotherapy, by injecting substances such as Radium-226 or Radium-223 for targeted treatment.
• Employed in industrial static eliminators by attracting free electrons and reducing static electricity.
• Provide energy for battery-powered pacemakers; Plutonium-238 alpha radiation is commonly used as the fuel source.
• Enable ionization smoke detectors, which utilize a tiny amount of Americium-241 to detect smoke by sensing ionization changes in air.

 

6. Match the names of outstanding Indian scientists given in List I with area of their specialized work given in List II and select the correct answer by using the codes given below the lists: [1998]

List-I List-II 
A. Dr. Raja Ramanna1. Plant chemistry
B. Dr. M.S. Swaminathan2. Nuclear physics
C. Prof. U.R Rao3. Thermodynamics & astrophysics
D. Prof. Meghnad Saha4. Space research
5. Agricultural science

Codes:

ABCD
(a)3521
(b)2143
(c)2543
(d)3142
Correct Answer: (c)
Solution:Raja Ramanna India's Most Eminent Nuclear Physicist, if we have today achieved the status of a "developed country" in nuclear science and technology, it is in large measure a consequence of Dr. Ramanna's ideals, policies and efforts. M. S. Swaminathan is an Indian agriculture scientist. He is known as the "Father of the Green Revolution in India." Udipi Ramachandra Rao is a space scientist and former chairman of the Indian Space Research Organisation. Prof Rao's experiments on a number of Pioneer and Explorer spacecrafts led to a complete understanding of the solar cosmic ray phenomena and the electromagnetic state of the interplanetary space. Meghnad Saha was an Indian astrophysicist, best known for his development of the Saha equation, used to describe chemical and physical conditions in stars.

7. Which one of the following elements is essential for the construction of nuclear reactors? [1998]

Correct Answer: (c) Zirconium
Solution:Zirconium is indispensable in the production of nuclear energy, particularly as a cladding for long cylindrical fuel rods inside nuclear reactors. There are several reasons why zirconium is an optimal material to surround uranium pellets: the metal is exceptionally resistant to corrosion and high temperatures, and it absorbs very few of the neutrons produced by a nuclear fission reaction. The latter is essential for the chain reaction to run effectively inside the reactor's core and to sustain the production of energy.

By cladding uranium fuel, zirconium also helps protect the coolant, typically water flowing through the reactor core, from contamination. It is estimated that up to 90 per cent of zirconium produced in the world is used for nuclear power.

8. Barium in a suitable form is administered to patients before an X-ray examination of the stomach, because : [1999]

Correct Answer: (c) barium is a good absorber of X-rays and this helps the stomach to appear clearly in contrast with the other regions in the picture.
Solution:Barium is given in adequate amount to patients before X-ray examination. The gut (gastrointestinal tract) does not show up very well on ordinary X-ray pictures. However, if you drink a white liquid that contains a chemical called barium sulphate, the outline of the upper parts of the gut (oesophagus, stomach and small intestines) shows up clearly on X-ray pictures. This is because X-rays do not pass through barium.

9. Cobalt-60 is commonly used in radiation therapy because it emits : [1999]

Correct Answer: (c) gamma rays
Solution:Gamma radiation from Cobalt-60 has high penetrating capability (each time an atom of Cobalt-60 decays, two high energy photons [1.17MeV and 1.33MeV] are emitted). An external sealed source of cobalt-60 is used in a teletherapy unit as a source of intense gamma radiation for the treatment of a variety of cancers. Cobalt-60 is also used as a medical tracer. A medical tracer is a material that is introduced into the body to make possible the observation of chemical, physical or biological processes in the body.

10. The following item consists of two statements. One labeled as the 'Assertion (A)' and the other as "Reason (R). You have to answer this item using the code given below: [2000]

Assertion (A): Large cold storage plants use ammonia as refrigerant while domestic refrigerators use chlorofluoro-carbons.

Reason (R): Ammonia can be liquefied at ambient temperature and low pressure.

Correct Answer: (a) Both A and R are true and R is the correct explanation of A
Solution:Ammonia is used as a large scale refrigerant because it has highest refrigerating capacity per pound of any refrigerant and a number of other excellent thermal properties that make it popular for a number of refrigeration applications in spite of its being toxic, explosive and flammable within certain conditions.

Ammonia is used as refrigerant prominently in the refrigeration systems of food industry like dairies, ice creams plants, frozen food production plants, cold storage warehouses, processors of fish, meat and number of other applications. Comparatively chlorofluorocarbon (CFC) chemical, safer refrigerators were possible for home and consumer use.