The correct option is B 2.94 s
Given:
Frequency, f = 1000 Hz
Wavelength, λ=34 cm=0.34 m
Distance to be travelled, s=1 km=1000 m
The wave speed is given by:
v=fλ
v=1000×0.34
v=340 ms−1
The time taken by the wave to travel 1 km is:
t=sv
t=1000340=2.94 s