A simple random sample consists of three observations 1, 3, 5. The point estimate of the population standard deviation is :

2

$\text{Sample observations: }1,3,5.$

$\bar{x}=\frac{1+3+5}{3}=3.$

$\sum (x-\bar{x})^2=(1-3)^2+(3-3)^2+(5-3)^2.$

$=4+0+4=8.$

$\text{Point estimate of population standard deviation}=\sqrt{\frac{\sum (x-\bar{x})^2}{n-1}}.$

$=\sqrt{\frac{8}{2}}.$

$=\sqrt{4}=2.$

$\text{Point estimate of population standard deviation}=2.$