423. Moon has no atmosphere because
   (a) it has no population
   (b) it is quite far off
   (c) its surface is full of rocks
   (d) its gravity is not sufficient for any atmosphere to hold on to it
Ans: (d)
424. The solar wind is composed of
   (a) outward stream of protons and electrons on the surface of the sun during
       solar flares and sun-spot activity
   (b) plasma
   (c) ionized gas
   (d) All of these
Ans: (a)
425. Which is the densest planet of the solar system?
   (a) Sun
   (b) Jupiter
   (c) Mercury
   (d) Earth
Ans: (d)
426. How is it that Pluto is not always the farthest planet of the solar system?
   (a) Each planet becomes the farthest planet in its turn. Now it is the turn of
   (b) The Sun is now in the zodiac in which it is nearest to outer planets
   (c) The eccentricity of Piuto"s orbit being substantial, this orbit cuts the orbit
       of Neptune
   (d) Piuto belongs to other solar system
Ans: (c)
427. The best estimates of the age of the earth comes from the studies of
   (a) angle of inclination of the earth
   (b) changes in radio-active minerals in it
   (c) period taken by Sun"s light to reach the earth
   (d) artificial satellites revolving round the earth
Ans: (b)