Which one of the following elements is essential for the construction of nuclear reactors?

(a) Cobalt

(b) Nickel

(c) Zirconium

(d) Tungsten

(c) Zirconium purified metal is primarily used by the nuclear industry to form the outer layer of fuel rods in nuclear reactors. Zirconium's major use is as cladding for nuclear reactors. It is ideal for this use, as it has a limited ability to capture neutrons, strength at elevated temperatures, considerable corrosion resistance, and satisfactory neutron damage resistance.

2. Barium in a suitable form is administered to patients before an X-ray examination of the stomach, because

(a) barium allows X-rays to pass through the stomach on account of its transparency to X-rays.

(b) barium is a good absorber of g-rays and this helps the stomach to appear clearly in contrast with the other regions in the picture.

(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.

(d) barium salts are white in colour and this helps the stomach to appear clearly in contrast with other regions in the pictures.

(c) 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 Xray pictures. This is because X-rays do not pass through barium.

3. Cobalt-60 is commonly used in radiation therapy because it emits

(a) alpha rays

(b) beta rays

(c) gamma rays

(d) X-rays

(c) Cobalt-60 is useful as a gamma ray source because it can be produced in predictable quantity and high activity by bombarding cobalt with neutrons. This is commonly used in radiation therapy for treatment of cancer.

4. 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.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

(a) 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.

5. Most of the explosions in mines occur due to the mixing of

(a) hydrogen with oxygen

(b) oxygen with acetylene

(c) methane with air

(d) carbon dioxide with ethane

(c) Mixing of methane with air is the cause of most mining explosions.