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?

(N/A) The neutron was discovered by James Chadwick.
$(b)$ According to Thomson's model of an atom,the negative and positive charges are equal in magnitude,which makes the atom electrically neutral as a whole.
$(c)$ The maximum number of electrons that can be accommodated in the outermost shell is $8$.
$(d)$ Atoms of different elements having the same atomic mass but different atomic numbers are called isobars.
$(e)$ $A$ hydrogen atom contains $0$ neutrons.