The product of the frequency and the wavelength of a wave equals the

a. number of waves passing a point in a second.
b. speed of the wave.
c. distance between wave crests.
d. time for one full wave to pass.

b. speed of a wave

Explanation:

The speed of a wave is defined as the product between the wave's frequency and the wave's wavelength:

where

is the wavelength of the wave

f is the frequency

Therefore, we see that this matches the definition listed in choice B:

b. speed of the wave.

The other options are:

a. number of waves passing a point in a second.  --> frequency

c. distance between wave crests.  --> wavelength

d. time for one full wave to pass. --> period

2.5metres

Explanation:

Wavespeed V = 350 m/s

Frequency = 140 Hz.

Wavelength = ?

Since, the wavelength is the distance covered by the wave in one complete cycle. It is measured in metres, and represented by the symbol λ.

So, apply the formula:

Velocity (V) = Frequency F x wavelength λ

350m/s = 140Hz x λ

λ = 350m/s / 140Hz

λ = 2.5 m

Thus, the wavelength of a wave is 2.5metres