$7.$ (a$ \leftrightarrow b) \leftrightarrow (a \oplus b)$
$8.$ ($\neg a \downarrow \neg b) \oplus \neg (a \oplus b)$
$9.$ (f $\leftrightarrow (a \vee b)) \oplus (\neg a \uparrow \neg b)$
$10.$ (a $\uparrow b) \uparrow (a \rightarrow b)$
$11.$ f $\vee ((a \rightarrow b) \downarrow (a \oplus b))$
$12.$ $(\neg (a \uparrow b) \rightarrow \neg(a \oplus b)) \vee ((a \oplus a) \rightarrow c)$
Have to tell if it is a tautology or contradiction and if not the model for 0 or 1.
So at 7 i would say it is either of em and the model for 1 is a=1 and b=1, for 0 a=0, b=0 For 8 i am stuck with the arrow trying to find out what that means.
