Answer:

Introduction:
Mirabilis jalapa, commonly known as the four o'clock plant, is a member of the Nyctaginaceae family. It is a popular garden plant due to its attractive and colorful flowers, which can be pink, red, yellow, white, or multicolored. The inheritance of flower color in Mirabilis jalapa follows a simple Mendelian pattern, making it an ideal model organism for genetic studies.

F1 Hybrid of Red and White Flowered Plants:
When a red flowered Mirabilis jalapa plant is crossed with a white flowered plant, the resulting F1 hybrid plants will have pink flowers. This is due to the incomplete dominance of the red flower color allele over the white flower color allele. In other words, the heterozygous F1 plants have a phenotype that is intermediate between the two homozygous parents.

Test Cross:
To determine the genotype of the F1 plants, a test cross can be performed. In a test cross, the F1 plants are crossed with a homozygous recessive plant (in this case, a white flowered plant). If the F1 plants are heterozygous (Rr), then half of the resulting offspring will have red flowers (Rr x rr = Rr and rr). On the other hand, if the F1 plants are homozygous dominant (RR), then all of the resulting offspring will have red flowers (RR x rr = Rr).

Percentage of Red Flowers:
Based on the above information, the percentage of red flowers in the test cross will depend on the genotype of the F1 plants. If the F1 plants are heterozygous (Rr), then 50% of the offspring will have red flowers. However, if the F1 plants are homozygous dominant (RR), then all of the offspring will have red flowers.

Conclusion:
In conclusion, the percentage of red flowers in the test cross of F1 hybrids of parental red flowered and white flowered Mirabilis jalapa plants will depend on the genotype of the F1 plants. If the F1 plants are heterozygous (Rr), then 50% of the offspring will have red flowers. However, if the F1 plants are homozygous dominant (RR), then all of the offspring will have red flowers.