Many theories and experiments carried out for the study of atom eventually led to the development of its structure. Arrange the given theories or models of atom proposed by different scientists in chronological order.
$\left(1\right)$ Planetary model
$\left(2\right)$ Watermelon model
$\left(3\right)$ Bohr's atomic model
$\left(4\right)$ Dalton's atomic theory

Rutherford's $\mathrm{\alpha }-$ray scattering experiment led to the discovery of the nucleus and to the conclusion that an atom consists of large empty space. Arrange the following steps in sequence which explains the experiment and also the above mentioned conclusions.
$\left(1\right)$ To make out the observations a spherical ZnS screen was placed surrounding the gold foil.
$\left(2\right)$ The substance which acts as a source of $\mathrm{\alpha }-$particles is taken in a lead container and made to pass through a slit between like charged positive plates.
$\left(3\right)$ It was observed that most of the particles passed straight through the gold foil, few were deflected through small angles and very few through large angles. Very few completely rebounded.
$\left(4\right)$ A narrow, condensed beam consisting of $\mathrm{\alpha } -$particles is made ot bombard on a thin a gold foil.

Assertion (A): Electrons present in ground states of different single electron species $\left(\mathrm{H}, {\mathrm{He}}^{+}, {\mathrm{Li}}^{++}\right)$ possess different amounts of energy.

Reason (R): Distances of electrons from the nuclei of different single electron species are equal.