On the basis of Rutherford's model of an atom,which subatomic particle is present in the nucleus of an atom?

Explain with examples $(i)$ Atomic number,$(ii)$ Mass number. Give any two uses of isotopes.

If $Z = 3$,what would be the valency of the element? Also,name the element.

If $K$ and $L$ shells of an atom are full,then what would be the total number of electrons in the atom?

Find out the mass number of oxygen and sulphur atoms.

If the number of electrons in an atom is $8$ and the number of protons is also $8$,then $(i)$ what is the atomic number of the atom? and $(ii)$ what is the charge on the atom?