Please understand that this is not a tutoring service. Also it is a fact that we have no idea upon what basis you are working.

Usually the definition is that in the real numbers if $A\subset B$ then $A$bis dense in $B$ means between any two members of $B$ there is an element of $A$.

As a basis for this study you should have worked out the properties of the integers.

This is the one you need for this question: if $x\in\mathbb{R}^+$ then then $\exists\left\lfloor x \right\rfloor\in\mathbb{N}$ such that $\left\lfloor x \right\rfloor\le x<\left\lfloor x \right\rfloor+1$; i.e. There is no integer between $n~\&~n+1$

Thus there can be no integer between $0~\&~1$.

I hope you see that there is no simple explanation?