Hygrometer is an instrument measure
A) Rainfall
B) Temperature
C) Humidity
D) None of these

Hint: Weather instruments can be used to take measurements of different atmospheric parameters at local weather stations. By understanding patterns of rainfall, temperature, humidity, and wind as measured by instruments, we can describe our local climate and weather.

Complete answer:
Weather instruments are used to take measurements of rainfall, temperature, wind, humidity, as well as many other atmospheric factors that describe the local climate and weather. The variables measured with these instruments are wind direction and speed, pressure, temperature, humidity, and precipitation, including snow and rain. The instrument used to measure relative humidity is called the hygrometer. Humidity is the measure of the amount of moisture in the air. An example of a hygrometer is the psychrometer. To measure relative humidity, a psychrometer uses two thermometers, one measures the wet-bulb temperature, and the other measures the dry-bulb temperature. The wet-bulb thermometer has water in the base which evaporates and absorbs heat by which temperature reading decreases. To determine relative humidity, the temperatures are taken from the dry-bulb thermometer and the temperature difference between the dry and wet bulb thermometers. From measurements obtained, a table is made up to find the relative humidity at any certain location. A thermometer is used to measure temperature. Rain gauges and snow gauges are used for measuring precipitation.
So, the correct answer is Option C.

Note: A sling psychrometer is the common instrument used to determine relative humidity. This instrument is swung while being held. There are varieties of other humidity sensors that work automatically to measure the relative humidity and water content of the atmosphere.