Which taxonomic category has its first letter written in capital case in binomial nomenclature?

Which of the following represents the correct sequence of taxonomic categories in descending order of variation?

$I$ - Species,$II$ - Kingdom,$III$ - Class,$IV$ - Genus,$V$ - Family,$VI$ - Phylum,$VII$ - Order
Categories classified based on similar characteristics - $P$
Categories classified based on a group of characteristics - $Q$
Select the correct option for $P$ and $Q$.
$P\quad\quad\quad\quad\quad Q$

$A$ group of plants with similar traits of any rank is known as:

In which of the following pairs of categories is it more difficult to determine the relationship to other taxa at the same level,thus making the problem of classification more complex?

What is the genus of tomato and brinjal?