In stratosphere, the excess refractive index is given as ________ in terms of refractive index .

In stratosphere, the excess refractive index is given as ________ in t

1.	In stratosphere, the excess refractive index is given as ________ in terms of refractive index .
A.	N=( -1) 10<sup>-6</sup>
B.	N=( -1) 10<sup>6</sup>
C.	N=(1+ ) 10<sup>-6</sup>
D.	N=( +1) 10<sup>6</sup>
Answer» B. N=( -1) 10<sup>6</sup>