According to Arrhenius equation, the plot of $\ln k$ vs $\frac{1}{T}$ yields a:

The Arrhenius equation is:
$$\ln k=\ln A-\frac{E_a}{RT}$$
Comparing with $y=mx+c$:$y=\ln k$, $x=\frac{1}{T}$, intercept $c=\ln A$, and slope $m=-\frac{E_a}{R}$.Since $E_a$ and $R$ are positive, the slope is negative. The plot is a straight line with a negative slope.