The expected values and variances for degree-based topological indices in three random chains*

This article is devoted to obtain a general method of calculating the expected values and variances for degree-based topological indices in random hexagonal, phenylene and polyphenyl chains. Based on the general method, some important degree-based topological indices are discussed and the explicit analytical expressions of their expected values and variances are presented, in which some known results are included. Besides, the expected values and variances for degree-based topological indices in these random chains are compared. In the end, the extremal values and the average values for degree-based topological indices in these random chains are determined.