A particle of mass \(M\) moves along a horizontal \(x\) axis from \(x = 0\) to \(x = L.\) The coefficient of kinetic friction varies as a function of \(x\) as \(\mu_k(x) = \mu_0 - \alpha x ,\) where \(\mu_0\) and \(\alpha\) are constants of appropriate dimensions, so that \(\mu _k(L) = 0.\) The total work done by the frictional force during the motion is \(n\mu_0MgL ,\) where \(g\) is the acceleration due to gravity. The value of \(n\) is:
1. \(\dfrac{1}{2}\)
2. \(3\)
3. \(1\)
4. \(\dfrac{1}{3}\)