Which of the following is true about the Laplacian spectrum 0=λ1≤λ2≤⋯≤λn0 = \lambda_1 \leq \lambda_2 \leq \dots \leq \lambda_n0=λ1≤λ2≤⋯≤λn of a graph GGG?
λ2>0\lambda_2 > 0λ2>0 if and only if the graph is connected
∑λi=n\sum \lambda_i = n∑λi=n
The number of connected components is equal to the number of eigenvalues equal to 1
λn≤n\lambda_n \leq nλn≤n