If the light wave has a wavelength of 10m what would be its velocity

The speed of light ... and all other forms of electromagnetic radiation ... depends only on the electrical properties of the medium, and not on wavelength.

The speed of light is

(299,792,458 m/s) / (index of refraction of the medium)

(The index of refraction of vacuum is 1.00 .  It's greater than 1.00 in any material stuff, and different in every material.)

= = = = =

By the way, an electromagnetic wave 10 meters long is no light wave.  It's a radio wave whose frequency is 30 MHz.

i think the answer is a, hope this is right, that would be my best guess.