Why did Rutherford select a gold foil in his $\alpha$-ray scattering experiment?

Answer the following in one line or one word:
$(a)$ Who discovered the neutron?
$(b)$ On the basis of Thomson's model of an atom,explain how the atom is neutral as a whole.
$(c)$ What is the maximum number of electrons that can be accommodated in the outermost shell of an atom?
$(d)$ What term is assigned to the atoms of different elements having the same atomic mass but different atomic numbers?
$(e)$ How many neutrons are present in a hydrogen atom?

In a sample of ethyl ethanoate $(CH_{3}COOC_{2}H_{5})$,the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

An atom of an element has full $K$ and $L$ shells and has $5$ electrons in its $M$ shell. What is its atomic number?

An alpha particle is also known as

Which of the $Na^+$ and $He$ has completely filled $K$ and $L$ shells? Give a reason to support your answer.