Only the standard Hermitian form is positive definite on $\mathbf C^2$

Which of the functions defines an inner product on $\mathbf C^2$? Let $x=[x_1,x_2]^t, y=[y_1,y_2]^t$. (i) $(x,y)=x_1\bar y_2$. (ii) $(x,y)=x_1\bar y_1+x_2\bar y_2$. (iii) $(x,y)=x_1y_1+x_2y_2$.