The wavelength of ultrasonic waves in air is of the order of [EAMCET 1989]

• A.            \[5\times {{10}^{-5}}\,cm\]   
• B.            \[5\times {{10}^{-8}}\,cm\]
• C.            \[5\times {{10}^{5}}\,cm\]     
• D.            \[5\times {{10}^{8}}\,cm\]