In the Doppler effect, does frequency change? Does wavelength change? Does wave speed change?

Solution 20RQ Doppler effect happens because of the relative motion between a source and an observer. Various cases are possible. For example, the source is at rest and the observer is moving, the observer is at rest and the source is moving, both source and observer are moving towards each other or moving away. Therefore, the frequency of the emitted wave by the source will change with respect to the observer. If the source moves towards the observer, frequency will increase. Otherwise it will decrease for the observer. This change in frequency will also result in a change in wavelength. With increase in frequency, wavelength will decrease and vice versa. Wave speed will not change as frequency increase (decrease) will be compensated by wavelength decrease (increase).