Choose the correct option for the following:
An instrument for detecting earthquakes is :

Question

Choose the correct option for the following: 
An instrument for detecting earthquakes is :

Accepted Answer

The correct answer to the question "An instrument for detecting earthquakes is:" is Option 3: A Seismograph.

1. **Explanation for Option 3 (A Seismograph):**
   A seismograph is a scientific instrument used to detect and record the vibrations and movements of the Earth's surface caused by seismic waves generated by earthquakes. It consists of a mass attached to a fixed base. During an earthquake, the base moves with the ground, but the mass does not, due to inertia. This relative motion is recorded and used to determine the strength and location of the earthquake. Seismographs are crucial for monitoring seismic activity and are widely used in the field of seismology.

2. **Explanation for why the other options are incorrect:**

- **Option 1 (A Fathometer):**
     A fathometer is an instrument used to measure the depth of water, typically in oceans or seas. It works by sending sound waves from a ship to the seabed and measuring the time it takes for the waves to return. This instrument is not related to detecting earthquakes and is used primarily in marine navigation and oceanography.

- **Option 2 (Lithoscope):**
     A lithoscope is not a standard term for any known scientific instrument, particularly in the context of detecting earthquakes. It may be confused with other geological or medical terms, but it does not pertain to seismology or earthquake detection.

- **Option 4 (Cardiograph):**
     A cardiograph, more commonly known as an electrocardiograph (ECG or EKG), is a medical instrument used to record the electrical activity of the heart. It is used in the field of medicine to diagnose heart conditions and has no application in detecting or recording seismic activity or earthquakes.

In conclusion, the seismograph is the only instrument among the given options that is specifically designed for detecting and recording earthquakes, making Option 3 the correct choice.