
$F=f l x g$
Weight of chain on table
$=$ Normal reaction of table
$=l(1-f) x g$
Friction acting on chain,
$f=\mu N=\mu l(1-f) x g$
in equilibrium,
$f=F \Rightarrow \mu l(1-f) x g=f l x g$
$\Rightarrow \quad \mu(1-f)=f \Rightarrow \mu=f(1+\mu)$
$\Rightarrow \quad f=\frac{\mu}{1+\mu} \Rightarrow f=\frac{1}{\left(1+\frac{1}{\mu}\right)}$



