Who discovered the neutron?

What is the ratio of the mass of a proton to the mass of an electron?

What are cathode rays?

Arrange the following particles in the increasing order of their $e/m$ ratio: electron $(e)$,proton $(p)$,neutron $(n)$,and $\alpha$-particle $(\alpha)$.

Proton is

In Millikan's experiment,static electric charge on the oil drops has been obtained by shining $X$-rays. If the static electric charge on the oil drop is $-1.282 \times 10^{-18} \ C,$ calculate the number of electrons present on it.