Under ideal conditions, how do allele frequencies change over time?
a. the allele frequency reaches over time.
b. the allele eventually reach a 50/50 balance.
c. the frequency of the dominant allele increases over time.
d. the frequency of the recessive allele increases over time.

Option D, The frequency of the recessive allele increases over time.

Explanation:

A dominant allele is usually expressed in a gene even if it present in pair with a recessive allele (until unless it is a co dominant species). While a recessive trait is expressed only when both alleles in a pair are recessive.  

Let us see through an example

Suppose both the male and female mating flower species are heterozygous dominant species. Thus,  only the dominant trait is expressed however the parent flowers also carry recessive allele.  

Let the male  flower be of  blue (Bb)  color and the female flower is also blue (Bb)

If a cross is carried out the between these two adults flowers, the following offspring are produced

Bb X Bb

BB, Bb. Bb, bb

The allele pair bb will produce white color flower.  

Hence with increase in time the frequency of the recessive allele increases