Best algorithm (Time Complexity) to find Minimum spanning tree of an complete, positive weighted, undirected, graph
Since it is a complete undirected graph, the number of edges are $\Theta(n^{2})$, where $n = |V|$. In order to find the MST, you must find the edge of minimum weight among all the given edges since it is always a part of the Minimum Spanning Tree. Since, the lower bound of finding the minimum among $N$ elements is $\Omega(N)$. Therefore, you can not do better than $\Omega(n^{2})$ if the graph is complete.