Which of the following is a common effect of a falling barometer?

A common effect of a falling barometer is the indication of approaching rain. A barometer measures atmospheric pressure, and a decrease in pressure typically suggests that a low-pressure system is moving in. Low-pressure systems are often associated with cloud formation and precipitation. As this system approaches, it usually brings moisture-laden air, leading to the likelihood of rain or storms.

Clear skies are more often associated with high-pressure systems, where the air is more stable and tends to discourage cloud formation. Cool temperatures can accompany various atmospheric conditions but are not directly linked to falling barometer readings. Similarly, decreasing humidity doesn't correlate as it is more common for humidity levels to rise as rain approaches with a falling barometer. Thus, the interpretation of falling barometer readings typically points to the imminent arrival of precipitation.