In Mendel's experiments with pea plants, the dominant trait for flower color is purple, while the recessive trait is white. When he crossed pure-breeding purple plants (homozygous dominant) with pure-breeding white plants (homozygous recessive), all the offspring in the F1 generation exhibited the dominant trait (purple flowers).
Thus, in the F1 generation, the phenotypic ratio expressed would indicate that all plants are purple, which can be described as a ratio of 4:0 for purple:white if considering a four-count total, but it is more common to represent this as simply 1:0 for the trait. Therefore, the ratio you are looking for that describes the dominant to recessive traits in that generation (F1) is effectively:
4:0 (if only these two categories are considered).
However, F2 generation ratios which include a typical Mendelian cross would show a 3:1 ratio of dominant to recessive after a self-fertilization of the F1 generation.
So, the direct answer from your options, based on the context, is: 4:0.