The correct option is A Factor
Based on the hybridisation experiments conducted by Mendel, he proposed that something is being passed on from one generation to the next unchanged via gametes.
He called them ‘factors’.
Factors are currently called genes and alleles are alternative forms of a gene. Genes are units of inheritance and they contain information required to express a particular trait.
Chromosomes are the condensed form of chromatin which contain DNA and proteins.