An instrument used in measuring the speed of wind is

Explanation

An anemometer is an instrument used to measure the speed of wind. It is a device that has cups that spin when the wind blows. The faster the wind blows, the faster the cups spin. The anemometer then calculates the wind speed based on the speed of the spinning cups. It is important to measure wind speed in various fields such as aviation, weather forecasting, and even sports. Wind speed affects the flight of planes, the accuracy of weather predictions, and the performance of athletes. The other options listed - a barometer, a wind gauge, a wind vane, and a hydrometer - are instruments used for other purposes and are not used to measure wind speed. Therefore, the correct option for the instrument used in measuring the speed of wind is option D, an anemometer.