Question

9.9% of dna is identical 0.1% is what helps us to differentiate between dna sequences

Answer 1

has 2 differences.

Obvious or obscure grouping

Often, individuals really group together quite naturally (if you perform a principle component analysis you will see clearly defined groups) but sometimes the groups are quite blurry.

The definition of species is arbitrary

Whether the grouping is blurry or not, it is often quite arbitrary how much two groups need to be different in order to classify them in different populations, different subspecies or different species, different genera, etc...