Explain why the barometer cannot be used to measure this pressure and state what would happen if an attempt?

A barometer measures the weight of a column of air above the instrument. In earth orbit this would not come into effect. The mercury would rise out of the tube and float about.

i'm not sure if the above answer is right as if there is a pressure then there is a weight of air above that point. what i think is more likely is that it is a slight 'trick' question. liquids will boil off at lower and lower temperatures as the air pressure around them drops (boiling of tea on mountains happens at 50ish degrees, for tall mountains anyway). so i suppose that it is all together possible that teh mercury will evaporate/boil and therefore not take the shape of teh bottom of the tube and hence be unable to measure the force pushing down on it. not sure about this either though!! CAN I JUST POINT OUT THAT THERE IS STILL GRAVITY IN SPACE - u would have to go to so called 'deep space' to have negligible gravity and therefore g=0

In a mercury barometer, the pressure of the air exactly counterbalances the pressure produced by a column of mercury. Air pressure can be produced by various causes and does not necessary require any gravity. However, the pressure produced by the mercury column depends on the mercury's weight. As a result, if you took the barometer into a weightless environment, the mercury column could not produce any pressure to counterbalance the air. what would happen is that the air pressure would force the mercury back up into the tube until there is no empty space left in the tube.