Which of these are created by changing magnetic and electric fields? 1.) radiations which travel with different speeds 2) compressions which travel with different speeds 3) transverse waves which travel with the speed of light 4) longitudinal waves which travel with the speed of sound

The two most prominent wavelengths in the light emitted by a hydrogen discharge lamp are 656(red) and 486 (blue). light from a hydrogen lamp illuminates a diffraction grating with 500 lines per mm, and the light is observed on a screen 1.50 behind the grating. what is the distance between the first-order red and blue fringes?