An ultraviolet wave traveling through a vacuum has a wavelength of 4.0 x 10-7m. The wave's frequency, written in scientific notation to two significant figures, is
x 10²4 Hz.

The formula you will need to solve this question is:

wavelength * frequency = speed of light

wavelength = 4.0*10^-7 m

frequency = f

speed of light = 3.0 * 10^-8 m/s

4.0 * 10^-7 m * f = 3.0 * 10^-8 m/s

f = 0.075 1/s = 0.075 Hz = 7.5 * 10^-2 Hz

Your final answer written in scientific notation to two significant figures is 7.5*10^-2 Hz.

I really hope this helps:)