If liquid $\mathrm{A}$ and $\mathrm{B}$ form ideal solutions then

We know that

In ideal solution there should not be any association between solute and solvent, that is there is no chemical interaction between solute and solvent of solution.

For Being an Ideal solution, A solution must obey these conditions:

$\mathrm{i})$There is no change in volume of mixing two components(solute and solvent) that is $\mathrm{\Delta V}=0$.

$\mathrm{ii})$There is no exchange of heat when the solute is dissolved in solvent $\mathrm{\Delta H}=0$.

${\mathrm{F}}_{\mathrm{A}-\mathrm{A}}={\mathrm{F}}_{\mathrm{B}-\mathrm{B}}={\mathrm{F}}_{\mathrm{A}-\mathrm{B}}$

Since, $\mathrm{\Delta H}=0,\mathrm{\Delta V}=0$

Then, the enthalpy of mixing is zero.

Hence, option(a) is correct.