The charge on an electron is equal to

State whether the following statement is true or false:
Each isotope of an element is an impure substance.

Complete the table on the basis of information available in the symbols given below:
$(a)$ ${ }_{17}^{35} Cl$
$(b)$ ${ }_{6}^{12} C$
$(c)$ ${ }_{35}^{81} Br$

Element	$n_{(p)}$	$n_{(n)}$

What are the postulates of Bohr's model of an atom?

Name any two noble gases.

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?