The diagram below shows a wave with its wavelength indicated in red.

When the wavelength of a wave is reduced by half, the frequency of the wave will increase. This is due to the relationship between wavelength (\( \lambda \)), frequency (\( f \)), and the speed of the wave (\( v \)), which is given by the equation:

\[ v = f \lambda \]

If the speed of the wave remains constant (which is true for a wave traveling through a uniform medium), reducing the wavelength will result in an increase in frequency to maintain the equation:

- If \( \lambda \) is halved, then \( f \) must double to keep \( v \) constant.

Therefore, the correct answer is:

**C. The frequency of the wave would increase.**