Those solutions in which there is no volume change upon mixing the components in the liquid state and which, when diluted do not undergo any heat change (i.e. heat of dilution is zero), are called __________ solutions.

For an ideal solution the heat of mixing or enthalpy change and volume change due to mixing is zero.
Since volume change mixing $$ = {V^t}\left( {T,P} \right) - \sum {} {x_i}{V_i}\left( {T,P} \right).$$
Where $${V^t} = $$   total molar volume of the solution at temperature $$T$$, pressure $$P$$.
$${V_i} = $$   molar volume of species when existed as pure species at same $$T$$, $$P$$
From summability : \[{{V}^{t}}=\sum{{}}{{x}_{i}}{{{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{V}}}_{l}}\]     where \[{{{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{V}}}_{l}}=\]  partial molar volume since for ideal solution
\[\sum{{}}{{x}_{i}}{{{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{V}}}_{l}}=\sum{{}}{{x}_{i}}{{V}_{i}}\left( T,P \right)\]       $$ \Rightarrow $$ Volume change of mixing $$= 0$$
Similarly, enthalpy change of mixing or heat of mixing $$= 0.$$