1. Let three complex numbers $1$, $\mathrm{i}$, and $z$ correspond to three collinear points in the complex plane, and $|z|=5$. Then $z=$ $\qquad$ .
1.4-3 i or $-3+4$ i.
Let $z=x+y$ i.
From the problem, we get $x+y=1$, and $x^{2}+y^{2}=25$.
Therefore, $(x, y)=(4,-3)$ or $(-3,4)$.