(c) the temperature at which the vapours of all liquid substances freeze
   (d) the temperature at which all substances exist in the vapour phase
Ans: (b)
154. One astronomical unit is the average distance between: [JPSC (Pre) 2011]
   (a) the Earth and the Sun
   (b) the Earth and the Moon
   (c) the Jupiter and the Sun
   (d) the Pluto and the Sun
Ans: (a)
155. Fish can survive inside a frozen lake, because [JPSC (Pre) 2011]
   (a) fish are warm-blooded animals
   (b) fish hibernate in ice
   (c) water near the bottom does not freeze
   (d) ice is a good conductor of heat
Ans: (c)
156. The S.I. unit of electric flux is :
   (a) Nm2/coul.
   (b) N coul/m2
   (c) Nm2/coul2
   (d) None of these
Ans: (a)
157. A hollow metal ball carrying an electric charge produces no electric field
   at points? [NDA 2010]
   (a) outside the sphere
   (b) on its surface
   (c) inside the sphere
   (d) only at the centre
Ans: (c)
158. The filament of an electric bulb is made of : [RRB ASM/GG 2003,2005,
   UPPCS (Pre) 2005]
   (a) copper
   (b) iron