Mercury is preferred as a barometric liquid because : (a) its density is high (b) its vapour pressure is negligible (c) it neither wets nor sticks to the glass (d) all of the above

(d) all of the above

Reason — Uses of mercury as a barometric liquid are —

1. The density of mercury is greater than that of any liquid, so only 0.76 m of the height of mercury is needed to balance the normal atmospheric pressure. Use of other liquids will require a much longer tube.
2. The vapour pressure of mercury is negligible, so the vapours in the Torricellian vacuum do not affect the barometric height.
3. Mercury neither wets nor sticks to the glass tube, therefore it gives an accurate reading.