Enzymes show the least amount of adaptation for which of the following?

In the modern system of nomenclature,which one of the following enzymes occupies the $1^{st}$ position?

$A$ - Activity of an enzyme can be affected by a change in environmental conditions.
$R$ - These factors regulate the activity of the enzyme.

Enzymes are proteins. Proteins are long chains of amino acids linked to each other by peptide bonds. Amino acids have many functional groups in their structure. Many of these functional groups are ionisable. As they are weak acids and bases in chemical nature,this ionisation is influenced by the $pH$ of the solution. For many enzymes,activity is influenced by the surrounding $pH$. This is depicted in the curve below. Explain briefly.

The curve given below shows enzymatic activity in relation to three conditions ($pH$,temperature and substrate concentration). What do the two axes ($x$ and $y$) represent?

The given graphical representation relates to enzyme activity under three conditions ($pH$,temperature,and substrate concentration). What do the given axes $X$ and $Y$ represent?
$X$-axis $-$ $Y$-axis