237. Which one of the following glasses is used in bullet proof screens? [NDA 2008]
     (a) Soda glass
     (b) Pyrex glass
     (c) Jena glass
     (d) Reinforced glass
Ans: (d)
238. Which substance is used to retard the setting action of cement? [NDA 2008]
     (a) CaO
     (b) AIO
     (c) CaSO.2HO
     (d) NaO + KO
Ans: (c)
239. What is a mixture of potassium nitrate, powdered charcoal and sulphur called? [NDA 2008]
     (a) Glass
     (b) Cement
     (c) Paint
     (d) Gun powder
Ans: (d)
240. Which one of the following is correct? Setting of Plaster of Paris is [CDS 2008]
     (a) dehydration
     (b) oxidation with atmospheric oxygen
     (c) hydration leading to another hydrate
     (d) combination with atmospheric
Ans: (b)
241. Which one of the following is a major constituent of Biogas? [CDS 2008]
     (a) Carbon dioxide
     (b) Methane
     (c) Hydrogen
     (d) Nitrogen dioxide
Ans: (b)
242. Which one of the following is not a chemical change? [CDS 2008]
     (a) Burning of coal in air
     (b) Fermentation of sugarcane juice
     (c) Crystallization of table salt from sea water
     (d) Cracking of petroleum
Ans: (c)
243. For which one of the following is the density maximum? [CDS 2008]
     (a) Chloroform
     (b) Water
     (c) Benzene
     (d) Ice
Ans: (b)
244. Which one of the following is the softest? [CDS 2008]
     (a) Sodium
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