Final answer:
The distance between the centers of two arms of a U-tube is affected by water pressure. The correct answer is b) Water pressure.
Step-by-step explanation:
The distance between the centers of two arms of a U-tube is not affected by a), c), or d).
b) The distance between the centers of two arms of a U-tube is affected by the difference in water pressure on each side. If the water pressure is higher on one side, it will cause the liquid to flow towards the side with lower pressure until the pressures are equal.
Therefore, the answer is Water pressure. If one side of a U-tube manometer is open to a gas container and the other to the atmosphere, the gas pressure can be determined by the height difference (h) of the fluid in the two arms and is given by the formula Pg = hpg, where Pg is the gauge pressure, h is the height difference, p is the density of the fluid, and g is acceleration due to gravity.
In the case of an open-ended manometer, the gas pressure is determined by this height difference plus the atmospheric pressure outside.