The sum-connectivity index of a graph G is defined as the sum of weights 1/root d(u) + d(v) over all edges uv of G, where du and dv are the degrees of the vertices u and v in G, respectively. In this paper, some extremal problems on the sum-connectivity index of trees are studied. The extremal values on the sum-connectivity index of trees with given graphic parameters, such as pendant number, matching number, domination number and diameter, are determined. The corresponding extremal graphs are characterized, respectively.
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