In the formula for Z-test statistic $Z=\frac{\overline{x}-\mu_0}{\frac{σ}{\sqrt{n}}}$, mark the incorrect statement.

$σ$ is variance of the population

Given Z-test statistic

$Z=\frac{\bar{x}-\mu_0}{\frac{\sigma}{\sqrt{n}}}$

Where

$\bar{x}$ = sample mean

$\mu_0$ = population mean

$n$ = sample size

$\sigma$ = population standard deviation

Thus the statement saying $\sigma$ is population variance is incorrect.

The incorrect statement is: $\sigma$ is variance of the population.