`IE_2` for `Zn` is comparatively lower as compared to other transition elements of same series.

Explanation

This is because `Zn^(c+)(3d^(10)4s^(1))` will readily lose an electron to acquire stable `3d^(10)` configuration.
`Zn(3d^(10)4s^(2))toZn^(2+)(3d^(10))+e^(e-)`