Answer:
2/4 or 1/2 of the F2 plants
Step-by-step explanation:
According to the given information, a cross between two heterozygous monohybrid with genotype "Rr" gives a F2 progeny. The genotype ratio of the obtained F2 progeny is 1 RR : 2 Rr : 1 rr.
Out of the total F2 progeny, 2/4 F2 plants are heterozygous dominant for the studied gene. Self crossing between two of these plants would produce the F3 progeny in 3 dominant: 1 recessive ratio.