Question

how do mendel's experiments show that the traits may be dominant or recessive

Answer 1

in mendels experiments alleses determine recessive and dominant traits

in an allele Tt  T determines dominant character here t is recessive

Answer 2

In the f1 generation the traits will be dominant as both the generations of plant is tall and in f2 generations the plants will be recessive as some of the plants were tall and some of this is dwarf in the ratio of 3:1
Tt determines dominant trait and tt determines recessive trait.