The chromosomal theory of inheritance was proposed by:

The correct answer is Option (2) → Walter Sutton

Option (2) Walter Sutton — Correct. Walter Sutton, with Theodor Boveri, saw that chromosomes behave in meiosis just as Mendel’s factors do. Sutton united chromosome movement with Mendel’s principles, which is called the chromosomal theory of inheritance.

NCERT Extract:
Chromosomal Theory of Inheritance – “… In 1900, three Scientists (de Vries, Correns and von Tschermak) independently rediscovered Mendel’s results on the inheritance of characters. Also, by this time due to advancements in microscopy that were taking place, scientists were able to carefully observe cell division. This led to the discovery of structures in the nucleus that appeared to double and divide just before each cell division. These were called chromosomes (colored bodies, as they were visualised by staining). By 1902, the chromosome movement during meiosis had been worked out. Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement (Figure 4.8) to explain Mendel’s laws (Table 4.3).”