What does '$X$' represent in the given figure?

Select the correct pair from the following.

Match the following columns and select the correct option based on the levels of biological organization and their corresponding scientific fields:

Column-$I$ (Scale)	Column-$II$ (Biological Level)	Column-$III$ (Science)
$a$. Macroscopic	$P$. Ecosystems	$i$. Physics
$b$. Submicroscopic	$Q$. Tissues	$ii$. Ecology
$c$. Conceptual	$R$. Organ systems	$iii$. Cytology
$d$. Microscopic	$S$. Subatomic particles	$iv$. Biology

Based on the levels of biological organization,what does the part labeled "$P$" indicate in the branches of science?

Assertion: Systematics is the branch of biology that deals with the classification of living organisms.
Reason: The aim of classification is to group the organisms.

Which of the following statements regarding nomenclature is correct?