If \( z \) and \( w \) are two complex numbers such that \( \left| zw \right| =1 \) and \( \text{arg}(z)-\text{arg}(w)=\cfrac { \pi }{ 2 } \), then
1
\( \overline { z } w=i \)
2
\( z\overline { w } =i \)
3
\( z\overline { w } =\cfrac { 1-i }{ \sqrt { 2 } } \)
4
\( z\overline { w } =\cfrac { -1+i }{ \sqrt { 2 } } \)