A satellite revolves round the earth. Air pressure inside the satellite is maintained at 76 cm of mercury. What will be the height of mercury column in a barometer tube 90 cm long placed in the satellite?

$\text{ inside the satellite }{\mathrm{g}}_{\mathrm{eff}}=0$

So, there will be no pressure difference inside the mercury. Hence the mercury will rise to full length of the tube, i.e., 90 cm because air pressure outside the tube is 76 cm of mercury, while pressure above the tube is zero.