Answer: C. lithium
Step-by-step explanation:
Standard reduction potential is the tendency for an element to gain electrons or get reduced ,measured at standard conditions i.e. when concentration is 1 M and temperature is 298 K.
It is given by:

![E^0_([Fe^(2+)/Fe])=-0.41V](https://img.qammunity.org/2017/formulas/biology/high-school/pno9iklyzm39kig712872mo3w4g1u4fjoo.png)
![E^0_([Li^(+)/Li])=-3.04V](https://img.qammunity.org/2017/formulas/biology/high-school/n3dsgbzhp3bbe9g56eqcwu3cbefkfv10fm.png)
![E^0_([Zn^(2+)/Zn])=-0.76V](https://img.qammunity.org/2017/formulas/chemistry/high-school/d4aj10xpmggrfo5ybce0v66w48n8ifjhdt.png)
Thus lithium has the lowest tendency to accept electrons and thus has lowest standard reduction potential.