Given ER diagram is 1:M relation.
For $R_2$ we need single table as we can combine $R_2$ with $R_{12}$
$T_1=(R_2,R_{12})$
Entity $R_1$ and attribute $B$ which is a multivalued attribute need a separate table.
$T_2=(R_1)$,
$T_3=(B)$
So total $3$ tables required.
Option $(3)$ is correct.