Bluebulb Projects' The Measure of Things presents:
25 is about one-fifth the number of Elements on the Periodic Table
In other words, it's 0.2120 times the count of Elements on the Periodic Table, and the count of Elements on the Periodic Table is 4.720 times that amount.
(a.k.a. Periodic Table of the Elements, a.k.a chemical elements) (confirmed elements as of 2016)