In an unbalanced three phase system, phase current $I_a=1\angle (-90^0) pu$ , negative sequence current $I_{b2}=4\angle (-150^0) pu$, zero sequence current $I_{c0}=3\angle (90^0) pu$. The magnitude of phase current $I_b$ in $pu$ is
1. $1.00$
2. $7.81$
3. $11.53$
4. $13.00$