Option 1: Dmitri Mendeleev was a Russian chemist who is best known for his development of the periodic table of elements. While Mendeleev`s work was influential in organizing the elements based on their atomic mass, he did not make the specific statement mentioned in the question.

Option 2: Henry Moseley, an English physicist, is credited with discovering the concept of atomic number. He conducted experiments involving X-rays and determined the atomic numbers of various elements. Moseley`s work showed that the order of elements on the periodic table should be based on atomic number rather than atomic mass. Therefore, Option 2 is the correct answer.

Option 3: J.J. Thomson was an English physicist who is best known for his discovery of the electron. While his work was important in understanding atomic structure, he did not specifically make the statement mentioned in the question.

Option 4: Ernest Rutherford, a New Zealand-born scientist, made significant contributions to our understanding of atomic structure. However, he did not make the specific statement mentioned in the question.

In conclusion, the correct answer is Option 2 as Henry Moseley is the scientist who made the statement that the atomic number of an element is a more fundamental property than its atomic mass.