If wavelength is doubled then frequency is: a. doubled. b halved. C unchanged. d quadrupled.

The correct answer is b. halved.<br /><br />When the wavelength of a wave is doubled, the frequency is halved. This is because the speed of a wave is constant, and the relationship between speed, wavelength, and frequency is given by the equation:<br /><br />Speed = Wavelength x Frequency<br /><br />If the speed remains constant and the wavelength is doubled, the frequency must be halved to maintain the equation's balance.