If the monohybrid cross between black male cat and brown female cat takes place, all offspring of #F_1# generation were black. Why were not brown offspring of #F_1# generation? Write down genotype ratio of second generation.?

Dominant traits - Seen in an individual with (Heterozygous) one or (Homozygous) two capital letter genes. (Aa, AA)
Recessive traits - Can only be seen with an individual who contains both small letter genes. (aa)

Consider this:
The father cat has a black/no color feature which is the dominant trait for this situation so his genotype could either be (BB) or (Bb).

The mother cat has a brown color feature which is recessive trait so the genotype is definitely (bb).

In the given, it is said that no offspring of theirs became brown.

If the monohybrid cross using Bb X bb was used, one offspring will become brown (Bb,Bb,Bb, bb) but if we use BB x bb, we will see that the dominant trait will suppress the brown trait for all 4 offspring (Bb, Bb, Bb, Bb) .

So what's the genotypic ratio of the F2 generation? The first one is the Homozygous dominant, second is heterozygous dominant and finally the homozygous recessive. So it will look something like this: 0:4:0
Meaning 0 homozygous dominant: 4 heterozygous dominant: 0 homozygous recessive.