For a two-level system, the weight of a given energy distribution can be expressed in terms of the number of systems, N, and the number of systems occupying the excited state, n1. What is the expression for weight in terms of these quantities

W = N! / (n0! * n1!)

Explanation:

Let n0 = number of particles in the lowest energy state

n1 = number of particles in the excited energy state.

Using this, we can say that N = n0 + n1

From this we can then express the weight, W of the close system by finding the factorials of each particles

W = N! / (n0! * n1!)

Hence, the weight W is expressed as W = N! / (n0! * n1!)