(a) electrons
   (b) neutrons
   (c) neutrons and electrons
   (d) electrons, neutrons and other particles
Ans: (b)
324. The nuclear model of atom was first visualised by
   (a) Rutherford
   (b) Neils Bohr
   (c) Albert Einstein
   (d) JJ Thompson
Ans: (a)
325. When the disturbed electrons of an exited atom transfer back into lower
   energy levels they emit energy in the form of electromagnetic wave pulses
   (a) neutrons
   (b) electrons
   (c) phonons
   (d) photons
Ans: (d)
326. The mass number and the atomic number of an element are X and Y
   respectively. The number of neutrons in the atom of that element is
   (a) X
   (b) Y
   (c) X + Y
   (d) X – Y
Ans: (d)
327. The electron has a mass equal to
   (a) 1.9 x 10-13 kg
   (b) 9.1 x 10-31 kg
   (c) 1 x 10-15 kg
   (d) 1.6 x 10-19 kg
Ans: (b)