What instrument is typically used to indicate atmospheric pressure in a coal mine?

The correct instrument used to indicate atmospheric pressure in a coal mine is a barometer. A barometer measures the pressure exerted by the atmosphere, which is crucial in mines for ensuring safe working conditions. Atmospheric pressure can influence ventilation and the behavior of gases, making it important for miners to monitor these levels.

In contrast, a manometer is typically used for measuring the pressure of gases or liquids in closed systems rather than the external atmospheric pressure. A thermometer measures temperature, which, while important in context, does not provide information about atmospheric pressure. A hygrometer, on the other hand, measures humidity and is not relevant to atmospheric pressure at all. Therefore, for monitoring the atmospheric pressure specifically in a coal mine, a barometer is the appropriate instrument.