If a pure tall plant is crossed with a pure dwarf plant, which trait will appear in the first generation?

Correct answer: Tall trait

In Mendel's pea plants, tallness is dominant over dwarfness. Represent the pure tall parent as TT and the pure dwarf parent as tt. Every offspring receives T from the first parent and t from the second, so all F1 plants are Tt. Because T masks t, all F1 plants show the tall phenotype. Therefore option B is correct.