The instrument to measure time is :

Options

A. barometer
B. chronometer
C. radiometer
D. None of these

Explanation

To solve the question regarding the instrument used to measure time, we can analyze the provided options step by step.

### Step 1: Understand the Options
We have three options:
1. Barometer
2. Chronometer
3. Radiometer

### Step 2: Analyze Each Option
- **Barometer**: This instrument is specifically designed to measure atmospheric pressure. It is not used for measuring time.

- **Chronometer**: This is a timekeeping device that measures time very accurately. It is often used in navigation and for scientific purposes to keep precise time.

- **Radiometer**: This instrument measures radiant energy or flux, not time. It is used in the study of light and energy.

### Step 3: Identify the Correct Instrument
From the analysis:
- The **Chronometer** is the only instrument among the options that is specifically designed for measuring time.

### Conclusion
The correct answer to the question "The instrument to measure time is:" is **Chronometer**.

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