Class XII

The isotope of uranium capable of sustaining chain reaction is
  1. U-235
  2. U-245
  3. U-239
  4. U-238
Which of the following has a least penetrating power?
  1. All have same penetrating power
  2. Beta Particles
  3. Alpha particles
  4. Gamma rays
The dark lines in the solar spectrum are due to
  1. . absorption of corresponding wavelengths by the outer layers of the sun
  2. destructive interference between waves of certain definite wavelengths
  3. . absorption of corresponding wavelengths by the prism used in the photograph
  4. absence of corresponding wavelengths from the light emitted by the core of the sun
In an atomic nucleus, neutrons and protons are held together by
  1. gravitational forces
  2. exchange forces
  3. coulombic forces
  4. magnetic forces
Atoms of an element differ from those of all other elements in
  1. atomic number and electronic configuration
  2. number of neutrons and number of valence electrons
  3. atomic number and number of valence electrons
  4. D. number of neutrons and electronic configuration
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