If the frequency of a dominant phenotype in a stable population is $75\%$, the frequency of recessive allele in that population would be

The correct option is D $50\%$
The given frequency of a dominant phenotype is $75\%$ and recessive will be $25\%$. 75 : 25 (i.e.,) 3 : 1 ratio which is AA, Aa, Aa . a. Here allele A : a is 4 : 4 (i.e.) 50 : 50.