A barometer tube reads 76 cm of mercury. If the tube is gradually inclined at an angle of 60° with vertical, keeping the open end immersed in the mercury reservoir, the length of the mercury column will be

The correct answer is 76 cm.

Step-by-step Explanation:
A barometer measures atmospheric pressure by balancing it against the weight of a column of mercury inside a tube. The hydrostatic pressure exerted by a liquid column depends solely on its vertical height, not on the inclination, length, or cross-sectional area of the tube.

The pressure ($P$) exerted by the mercury column is given by the formula:

$P=\rho gh$

where:
• $\rho$ is the density of mercury,
• $g$ is the acceleration due to gravity, and
• $h$ is the vertical height of the mercury column.

Since the atmospheric pressure, the density of mercury, and the acceleration due to gravity remain constant, the vertical height ($h$) of the mercury column must also remain constant to balance the atmospheric pressure. Therefore, even when the tube is gradually inclined at an angle of 60° with the vertical, the vertical height of the mercury column remains unchanged at 76 cm.