Which enzymes are responsible for changing the arrangement of atoms in substrate molecules?

The activity of an enzyme is sensitive to the presence of specific chemicals,which is called:

What are the different classes of enzymes? Explain any two with the type of reactions they catalyse.

At a temperature just below the freezing point,the enzyme:

Select the correct match for $X$ and $Y$:

Column $X$	Column $Y$
$(1)$ Aldolase	$(P)$ Hydrolases
$(2)$ Hexokinase	$(Q)$ Ligases
$(3)$ Succinic dehydrogenase	$(R)$ Lyases
$(4)$ Fructose isomerase	$(S)$ Oxidoreductases
$(5)$ Lactase	$(T)$ Transferases
$(6)$ Acetyl $CoA$ synthetase	$(U)$ Isomerases

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