The second generation phenotypes resulting from the cross of purebred monohybrid pollination will display a ratio of 2: 2 4: 1 3: 1 none of the above

The answer is 3:1.

If we imagine that plant has two alleles for the trait, we can dominant allele represent with P represents and recessive allele with p. To get purebred monohybrid in the first generation, parents must be a dominant homozygote (PP) and a recessive heterozygote (pp):

Parental generation: PP   x   pp
The first generation: Pp  Pp  Pp  Pp

Pp represents a heterozygote.
If we cross these heterozygotes:

The first generation: Pp   x   Pp
The second generation: PP  Pp  Pp  pp

If dominant allele determines the phenotype, there will be 3 plants (one PP and two Pp) with one phenotype and only 1 plant (pp) with another phenotype and vice versa.