The correct answer is: B. Hygrometer.
A hygrometer is a device used to measure the amount of water vapor in the air. There are many different types of hygrometers, but they all work by measuring the amount of water vapor in the air and converting it into a reading.
A hydrometer is a device used to measure the density of liquids. It does
not measure humidity.A psychometer is a device used to measure the wet-bulb and dry-bulb temperatures of the air. The wet-bulb temperature is the temperature of the air when it is saturated with water vapor. The dry-bulb temperature is the temperature of the air when it is not saturated with water vapor. The difference between the wet-bulb and dry-bulb temperatures can be used to calculate the relative humidity of the air.
An anemometer is a device used to measure wind speed. It does not measure humidity.