HELLO RANJEET
Well i find the comment posted by gokul boro very useful in this regard. If you see the the frequency spacing between two consecutive subcarriers is 1.25 GHz and he’s right that the subcarriers are numbered like 1,2..so on . By multiplying the each of them by frequency gap, we get 1.25 GHZ 2.50 GHz respectively. I feel this should be enough for you to understand.
Thanks and regards