An elementary particle is:

The neutrino has:

What are cathode rays? Write down their characteristics.

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 ........... .

$(i)$ Calculate the number of electrons which will together weigh $1 \, g$.
$(ii)$ Calculate the mass and charge of one mole of electrons.

Write down the results of the cathode ray discharge tube experiment.