f = frequency of the buzzing sound of honey bees = 2.3 x 10² Hertz
T = Time period of a bee's wing beat
The Time period of bee's wing beat is inversely related to frequency and is given as
T = 1/f
inserting the values
T = 1/(2.3 x 10²)
T = 4.35 x 10⁻³ seconds
hence the correct choice is
a. 4.3x10^-3