Question

what type of mirror are used in car  head lights?                                                                       observe values in which material velocity of lightn is necessary?
(1)m=1.31->ice
(2)carbon disulphide-u=1.83

Answer 1

A Concave mirror can be used in car head lights

1) So u = c/v where c = speed of light in vacum and v = speed of light in substance

1.31 = 3 x 10⁸/v
v = 2.29 x 10⁸ m/s

2) 1.83 = 3 x 10⁸/v
  v = 1.64 x 10⁸ m/s

Answer 2

The mirror used in a car headlight is the Concave spherical mirror. The reason is that:  the bulb is placed nearly at the focus of the concave mirror.  The light rays get reflected parallel to the axis of the mirror.   Now the headlight is inclined at a small angle to the road and so they fall on the road at a long distance from the car like 30 to 40 meters.

The language in the question is not clear.. But I assume the following: 

I assume that the values given are the refractive indices of the media.
         μ = 1.31    for ice.
    μ = speed of light in vacuum / speed of light in the medium
       speed of light in ice = (3 * 10⁸ m/s)  / 1.31 = 2.29 * 10⁸ meters/sec

2) carbon di-sulfide has a refractive index = 1.83

      speed of light in Carbon di-sulfide = 3 * 10⁸ / 1.83 = 1.639 * 10⁸ m/sec