The first model of an atom was given by

Rutherford's $\alpha$-particle scattering experiment showed that:
$(i)$ electrons have negative charge
$(ii)$ the mass and positive charge of the atom is concentrated in the nucleus
$(iii)$ neutron exists in the nucleus
$(iv)$ most of the space in the atom is empty
Which of the above statements are correct?

How did Rutherford prove that positively charged particles are present in the nucleus of an atom?

$(a)$ What are canal rays? Who discovered them? What is the charge and mass of canal rays?
$(b)$ How are the canal rays different from electrons in terms of charge and mass?

$(a)$ Define the following terms with one example each:
$(i)$ Isotope
$(ii)$ Isobar
$(b)$ Name the elements whose isotopes are used in:
$(i)$ Nuclear Reactor
$(ii)$ Treatment of cancer

What are isobars? Give one example.