The speed of sound can be calculated using the formula \( v = f \lambda \), where \( v \) is the speed, \( f = 500 \, \text{Hz} \) is the frequency, and \( \lambda = 0.68 \, \text{m} \) is the wavelength. Substituting the given values yields \( v = 500 \times 0.68 = 340 \, \text{m/s} \). Therefore, the speed of sound in air is \( 340 \, \text{m/s} \).