A and b can't be right answer. so there is confusion in c and d , but option c is correct becoz auxanometer is used to measure growth of plants and manometer id used to pressure between two points.
so manometer is used to measure root pressure in plants.

Root pressure is the force exerted by the roots of a plant to push water and nutrients upwards through the xylem vessels. It is an important mechanism for water uptake in plants, especially in situations where transpiration rates are low, such as during the night or in humid conditions.

Measurement of root pressure is typically done using a manometer, which is a device that measures pressure. A manometer consists of a U-shaped tube partially filled with a liquid, such as mercury or water, and connected to the plant root system. The height difference of the liquid in the two arms of the U-shaped tube indicates the pressure exerted by the roots.

The correct answer to the given question is option 'c' - Manometer. Let's understand why:

Manometer:
- A manometer is a device used to measure the pressure of a fluid, in this case, the root pressure in plants.
- It consists of a U-shaped tube filled with a liquid, with one end connected to the plant root system and the other end open to the atmosphere.
- The liquid in the tube moves up or down depending on the pressure exerted by the roots.
- The height difference of the liquid in the two arms of the U-shaped tube is measured to determine the root pressure.

Other options explained:
a) Barometer:
- A barometer is a device used to measure atmospheric pressure and is not suitable for measuring root pressure.
- It is typically used to predict weather changes.

b) Atmometer:
- An atmometer is a device used to measure the rate of evaporation from a plant's surface.
- It is not directly related to measuring root pressure.

d) Auxanometer:
- An auxanometer is a device used to measure the growth of plants or plant parts.
- It is not used for measuring root pressure.

In conclusion, root pressure is measured using a manometer, as it allows for the measurement of the pressure exerted by the roots in pushing water upwards through the plant's vascular system. Other options such as barometer, atmometer, and auxanometer are not suitable for measuring root pressure.