Who provided the experimental verification of the chromosomal theory…

The correct answer is Option (2) → Thomas Hunt Morgan

Sutton and Boveri saw that chromosomes pair and separate in meiosis just as Mendel’s factors do. Sutton joined this idea with Mendel’s principles as the chromosomal theory of inheritance. The theory was then proved by experiment by Thomas Hunt Morgan and his colleagues, who worked with the fruit fly Drosophila melanogaster. The fly suits such work: it grows on a simple medium, completes its life cycle in about two weeks and gives many offspring.

NCERT Extract:
Chromosomal Theory of Inheritance – “… Sutton and Boveri argued that the pairing and separation of a pair of chromosomes would lead to the segregation of a pair of factors they carried. Sutton united the knowledge of chromosomal segregation with Mendelian principles and called it the chromosomal theory of inheritance. Following this synthesis of ideas, experimental verification of the chromosomal theory of inheritance by Thomas Hunt Morgan and his colleagues, led to discovering the basis for the variation that sexual reproduction produced.”