c
(c)
Ref. image $I$
Given that acceleration of block B is $2 m / sec ^2$
Drawing $FBD$ of $A$ ref. image $II$
$f _2$ frictional force due to $B$
Now $=\frac{ f }{ m }= a$
$\Rightarrow \frac{ f }{5}=2$
$\Rightarrow f _2=10\,N$
$10\,N$ of frictional force is applied by $B$ on $A$
