A uniform chain of length 'l' is placed on a rough table, with its length $\large\frac{l}{n} ( n > 1)$ hanging over the edge of the table. If the chain just begins to slide off the table by itself, the coefficient of friction between the chain and the table is :

Question

$\begin {array} {1 1} (1)\;\large\frac{1}{n+1} & \quad (2)\;\large\frac{1}{n-1} \\ (3)\;\large\frac{n-1}{n+1} & \quad (4)\;\large\frac{1}{n} \end {array}$