212. Which one of the following. When dissolved in HO gives hissing sound? [CDS 2009]
     (a) Limestone
     (b) Slacked lime
     (c) Soda lime
     (d) Quicklime
Ans: (a)
213. The rusting of iron nail [CDS 2009]
     (a) decreases its weight
     (b) increases its weight
     (c) does not affect weight but iron is oxidized
     (d) does not affect weight but iron is reduced
Ans: (b)
214. Which one of the following heavy water is used in nuclear reactor? [CDS 2009]
     (a) Water having molecular weight 18 amu
     (b) Water having molecular weight 20 amu
     (c) Water at 4°C but having molecular weight 19 amu
     (d) Water below the ice in a frozen sea
Ans: (b)
215. Which one of the following is used as a mordant in dying and tanning industry? [CDS 2009]
     (a) Magnesium oxide
     (b) Magnesium carbonate
     (c) Magnesium chloride
     (d) Magnesium sulphate
Ans: (d)
216. What are Rubies and Sapphires chemically known as? [IAS 2008]
     (a) Silicon dioxide
     (b) Aluminium oxide
     (c) Lead tetra oxide
     (d) Boron nitride
Ans: (b)
217. Which one of the following is also called Stranger Gas? [IAS 2008]
     (a) Argon
     (b) Neon
     (c) Xenon
     (d) Nitrous oxide
Ans: (c)
218. Mixture of which one of the following pairs of gases is the cause of occurrence of most of the explosions in mines? .
     [IAS 2008]
     (a) Hydrogen and oxygen
     (b) Oxygen and acetylene
     (c) Methane and air
     (d) Carbon dioxide and methane
Ans: (c)