We know that number of edges in any spanning tree is m-1. Here m is the number of vertices. Now, it is also known that if you remove any 1 vertex from spanning tree will make the graph disconnected. Now the number of edges which are not part of spanning tree will be mC2-(m-1).
Here mC2 is maximum number of edges possible in a graph.
Therefore, removing
(mC2-(m-1))+1 edges will always guarantee that graph will be disconnected.
In the question, option should be
mC2-m+2.