241 .The mass number of an atom is determined by-
A.  Adding the number of neutrons and number of electrons
B.  Adding the number of protons and number of electrons
C.  The number of protons only
D.  Adding the number of neutrons and number of protons
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242 .A deep sea driver may hurt his ear drum during diving because of
A.  lack of oxygen
B.  high atmospheric pressure
C.  high water pressure
D.  All of the above
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243 .Velocity of sound in air
(i) increases with temperature
(ii) decreases with temperature
(iii) increase with pressure
(iv) is independent of pressure
(v) is independent of temperature

A.  Only (i) and (ii) are true
B.  Only (ii) and (iv) are true
C.  Only (i) and (iii) are true
D.  Only (i) and (iv) are true
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244 .It is difficult to cook at high altitudes because
A.  there is less oxygen in the air
B.  due to falling temperature, more heat has to be given
C.  due to decrease in atmospheric pressure, the boiling point of water decreases
D.  of high moisture content there
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245 .The depletion of Ozone layer is mainly due to-
A.  Radioactive rays
B.  Chloroflurocarbons
C.  Volcanic Eruptions
D.  Aviation fuels
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246 .A symbiotic relationship in which both species benefit is best described as _______.
A.  Commensalism
B.  Competative exclusion
C.  Parasitism
D.  An obligatory relationship
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247 .In optical instrument, the lenses are used to form image by the phenomenon of -
A.  reflection
B.  refraction
C.  scattering
D.  diffusion
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248 .If there were no atmosphere, the length of the day on the earth will
A.  decrease
B.  increase
C.  remain the same
D.  none of these
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249 .The resistance of an ideal ammeter is
A.  zero
B.  very low
C.  very high
D.  infinite
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250 .The most penetrating radiation out ofthe following is
A.  X - rays
B.  α – rays
C.  β rays
D.  γ rays
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