Rainfall is measured by an instrument called the ______.

rain gauge

The correct answer is option 1. rain gauge.

A rain gauge is a meteorological instrument used to measure the amount of precipitation (rainfall) over a specific period of time at a particular location. It consists of a cylindrical container with a funnel-shaped top that collects rainwater. The rainwater collected in the container is then measured using a calibrated scale, typically marked in millimeters or inches, to determine the amount of rainfall.

Rain gauges can come in various designs, but they all function based on the principle of collecting and measuring the amount of water that falls within a defined area. This information is crucial for weather monitoring and forecasting, agriculture, hydrology, and various other fields that rely on accurate precipitation data.