To determine the time it takes for a sound wave to travel a certain distance, we can use the formula:

Time = distance/speed

In this case, the distance is given as 2.4 km. However, the speed of sound is not given directly, but we can calculate it using the formula:

Speed = frequency x wavelength

The frequency is given as 4 kHz, which can be converted to 4000 Hz. The wavelength is given as 30 cm, which can be converted to 0.3 m.

Therefore, the speed of sound can be calculated as:

Speed = 4000 Hz x 0.3 m = 1200 m/s

Now that we have the speed, we can substitute it into the formula for time:

Time = 2.4 km / 1200 m/s = 2000 m / 1200 m/s ≈ 1.67 s

Rounding to the nearest whole number, the time it takes for the sound wave to travel 2.4 km is approximately 2.0 s. Therefore, Option 1, 2.0 s, is the correct answer.