For ideal solution, we have

$\Delta$H_mix = 0, $\Delta$V_mix = 0

Now U_mix = ∆H_mix – P$\Delta$V_mix

$\therefore$ $\Delta$U_mix = 0

Also, for an ideal solution,

p_A = x_Ap_A^o, p_B = x_Bp_B^o

$\therefore$ $\Delta$p = p_observed – p_calculated = 0

$\Delta$G_mix = $\Delta$H_mix – T$\Delta$S_mix

For an ideal solution, $\Delta$S_mix $\ne$ 0

$\therefore$ $\Delta$G_mix $\ne$ 0