Let's analyze each statement to identify the incorrect one:

Option A: The acidic strength of $$\mathrm{HX}(\mathrm{X}=\mathrm{F}, \mathrm{Cl}, \mathrm{Br}$$ and $\mathrm{I})$ follows the order: $$\mathrm{HF}>\mathrm{HCl}>\mathrm{HBr}>\mathrm{HI}$$.

This statement is incorrect. The correct order of acidic strength for hydrohalic acids is $$\mathrm{HF} < \mathrm{HCl} < \mathrm{HBr} < \mathrm{HI}$$. This is because as we move down the group, the bond strength between hydrogen and the halide decreases, making it easier to ionize in water and making the acid stronger.

Option B: Fluorine exhibits $-1$ oxidation state whereas other halogens exhibit $+1, +3, +5$ and $+7$ oxidation states also.

This statement is correct. Fluorine is the most electronegative element and can only exhibit $-1$ oxidation state. Other halogens can exhibit positive oxidation states due to the availability of d-orbitals.

Option C: The enthalpy of dissociation of $\mathrm{F}_2$ is smaller than that of $\mathrm{Cl}_2$.

This statement is correct. The bond dissociation energy of $\mathrm{F}_2$ is indeed smaller than that of $\mathrm{Cl}_2$ because the F-F bond is weaker due to significant electron-electron repulsion between the non-bonding electrons in the small fluorine molecule.

Option D: Fluorine is a stronger oxidising agent than chlorine.

This statement is correct. Fluorine is the most electronegative element, which makes it the strongest oxidizing agent among the halogens.

Therefore, the incorrect statement is Option A.