f the coefficient of the $5^{th}$ term be the numerically the greatest coefficient in the expansion of $(1-x{)}^n$, then the positive integral value of $n$, is 

We know that the coefficient of the middle term is 

the numerically greatest coefficient in the expansion of $(1-x{)}^n$

or ${( 1+x )}^n$ and its value is  ${ }^n{C}_{n/2}$ or,$\frac{{ }^n{C}_{n+1}}{2}=\frac{{ }^n{C}_{n-1}}{2}$according 

as $n$ is even or odd. 

It is given that the coefficient of the $5^{th}$ term is the greatest. 

Therefore, $5^{th}$ term is the middle term. Thus, there are $9$terms.

Hence $n = 8.$