Atmospheric Pressure in Closed Manometer

Steps:

• A sealed-end manometer measures absolute atmospheric pressure; the sealed side is vacuum.
• Atmospheric pressure pushes mercury up the sealed tube, creating height difference h.
• h equals P_atm / (ρg), where ρ is mercury density and g is gravity.
• At higher altitude, P_atm decreases, so h decreases.

Why A is correct:

• Boyle's law and barometric formula show P_atm drops with height, reducing h in the manometer equation.

Why the others are wrong:

• B: Atmospheric pressure decreases, not increases, with height.
• C: Atmospheric pressure decreases, not increases, with height.
• D: Decreased pressure causes h to decrease, not increase.

Final answer: A