Atomic models have been improved over the years. Arrange the following atomic models in their chronological order:
$(i)$ Rutherford's atomic model
$(ii)$ Thomson's atomic model
$(iii)$ Bohr's atomic model

Which of the following statements are true for an element?
$(i)$ Atomic number $=$ number of protons $+$ number of electrons
$(ii)$ Mass number $=$ number of protons $+$ number of neutrons
$(iii)$ Atomic mass $=$ number of protons $=$ number of neutrons
$(iv)$ Atomic number $=$ number of protons $=$ number of electrons

State whether the following statement is true or false:
In a chemical substance,the elements are always present in varying proportions by mass.

$(a)$ Explain why did Rutherford select a gold foil in his alpha scattering experiments?
$(b)$ What observations in $\alpha$-scattering experiment led Rutherford to make the following conclusions?
$(i)$ Most of the space in an atom is empty.
$(ii)$ Nucleus is positively charged.
$(c)$ Mention any two drawbacks of Rutherford's model.

State three rules suggested by Bohr and Bury for the distribution of electrons into different orbits (shells) of an atom.

$(a)$ Name the three subatomic particles of an atom.
$(b)$ An atom of an element has $5$ electrons in the $L$ shell.
$(i)$ What is the atomic number of the element?
$(ii)$ State its valency.
$(iii)$ Identify the element and write its name.