The volume occupied by the nucleus is about $ . . . . . . $ times the volume of an atom.

Which is the correct statement about a proton?

Fill in the blanks:
$(i)$ $R. A. Millikan$ developed the ......... method to determine the charge of an electron.
$(ii)$ The positively charged particles in a modified cathode ray tube are called ............ .
$(iii)$ The smallest and lightest positive ion obtained from hydrogen is ........... .
$(iv)$ In the year $1932$,$Chadwick$ discovered ........... .

When beryllium is bombarded with $\alpha$-particles,extremely penetrating radiations which cannot be deflected by electrical or magnetic field are given out. These are

Who determined the charge-to-mass ratio $(e/m_e)$ of an electron and how? Explain.

The positron was discovered by