#### Answer

$0.927\ mm$

#### Work Step by Step

Mass of mercury: $3.416-3.263=0.153\ g$
Density of mercury: 13.546 g/cm³, so the volume is:
$V=m/\rho=0.0113\ cm^3$
Length of the tube $16.75\ mm = 1.675\ cm$
Volume of the tube: $V=\pi r^2 L$, so the radius is:
$r=0.0463\ cm=0.463\ mm$
So the diameter (twice the radius) is $0.927\ mm$.