This is the reason why Mendel did not recognize linkage phenomenon in his experiments

The correct option/answer is: "characters he studied were situated on different chromosomes".

Gregor Mendel formulated the laws of inheritance, including the Law of Independent Assortment. This law states that alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

Linkage, on the other hand, is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. When genes are located on the same chromosome and are physically close to each other, they do not assort independently because they are linked.

Mendel did not observe or recognize the linkage phenomenon in his experiments because the seven distinct traits (characters) he selected for study in the garden pea (Pisum sativum) were controlled by genes located on different chromosomes (or were so far apart on the same chromosome that they behaved as if they were on different chromosomes, assorting independently).

Because these genes were situated on different chromosomes, they sorted independently during gamete formation, which perfectly aligned with his Law of Independent Assortment and prevented him from detecting any deviations caused by genetic linkage.