Mendel observed red flowers in F1 when he crossed red and white flowered plants because of
When a homozygous red flowered plant(RR) is crossed with another homozogyous white flowered(rr) plant. The F1 progeny shows Red flowers, because Red colour is the dominant character over white colour. It is called Law of dominace.
Mendel postulated that, When two contrasting alleles for a character are brought together in an organism, only one is expressed completely and shows visible effect, second one cannot. The allele, expressed its character is called dominant allele and other one is recessive allele. This is called Law of dominance.
So, the correct option is ‘Dominance’.