(b) 2 only
     (c) Both 1 and 2
     (d) Neither 1 nor 2
Ans: (d)
225. Which of the following statements regarding carbon dioxide is/are correct? [NDA 2008]
          1) It is prepared on large scale by the action of water on lime.
          2) In the solid form it can be used as a refrigerant.
     (a) 1 only
     (b) 2 only
     (c) Both 1 and 2
     (d) Neither 1 nor 2
Ans: (b)
226. In which one of the following situations a chemical reaction does not occur? [NDA 2008]
     (a) Common salt is exposed to air
     (b) Coal is burnt in air
     (c) Sodium is placed in water
     (d) Iron is kept in moist air
Ans: (a)
227. Which one of the following materials is suitable for water purification? [NDA 2008]
     (a) Silicones
     (b) Zeolites
     (c) Asbestos
     (d) Quartz
Ans: (b)
228. Why do two ice blocks join to form one block when pressed together? [NDA 2008]
     (a) Melting point of ice is lowered with increase in pressure
     (b) Melting point of ice increases with increase in pressure
     (c) Melting point of ice remains unchanged with increase in pressure
     (d) Melting point of ice is 0°C
Ans: (a)
229. Some common mediums in which speed of sound waves is measured are mentioned below:
     1) Air
     2) Steel
     3) Copper
     4) Water
     What is the correct increasing order of the speed of sound? [NDA 2008]
     (a)  1<4<2<3
     (b)  4<1<2<3
     (c)  1<4<3<2
     (d)  4<1<3<2
Ans: (c)
230. Which one of the following chemicals is used in foam fire extinguishers? [NDA 2008]
     (a) Aluminium sulphate
     (b) Copper sulphate
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