To determine the appropriate tool for Sian to measure the number of seconds it takes for the contents of a beaker to change from clear to purple, let’s examine the purpose of each tool listed in the options:
1. An electronic balance: This tool is used for measuring mass. It determines the weight of an object placed on it. Therefore, it is not suitable for measuring time.
2. A stopwatch: This is a timekeeping device specifically designed to measure the amount of time that elapses between its activation and deactivation. This tool is indeed used for measuring time, making it a strong candidate for Sian's needs.
3. A barometer: This instrument measures atmospheric pressure. It is commonly used in weather forecasting and is unrelated to the measurement of time.
4. A graduated cylinder: This is a piece of laboratory equipment used to measure the volume of a liquid. It has markings indicating volume increments. This tool does not measure time.
After analyzing the options, the most appropriate tool for Sian to use to measure the number of seconds it takes for the contents of the beaker to change color is a stopwatch. Thus, the correct answer is:
○ a stopwatch.
