343. The phenomenon of radioactivity was discovered by
   (a) Rutherford
   (b) Bohr
   (c) Henri Bacquerel
   (d) Marie Curie
Ans: (c)
344. Out of the following which element has the longest half-life period?
   (a) Radium
   (b) Radon
   (c) Uranium-238
   (d) Plutonium
Ans: (c)
345. Isotones are species of atoms containing
   (a) same number of protons but different number of neutrons
   (b) same number of neutrons but different number of protons
   (c) the same total number of protons and neutrons
   (d) same number of protons and different number of electrons
Ans: (b)
346. The end product in the uranium disintegration series is
   (a) lead
   (b) zinc
   (c) carbon
   (d) tin
Ans: (a)
347. Antiparticle of electron is
   (a) proton
   (b) antiproton
   (c) positron
   (d) neutron
Ans: (c)
348. Electron-volt is a unit of
   (a) power