Therefore y_{0} = [I/(2p^{2}rvf^{2})]^{1/2}

Density of water = 1000 kg/m^{3}

Speed of sound in water = 1550 m/s

y_{0} = [(1.5X10^{-5} W/m^{2})/(2p^{2}X1000
kg/m^{3}X1550 m/s(60X10^{3} Hz)^{2})]^{1/2}
= 1.2X10^{-11} m

Answer is A