How many pairs of letters are there in the word ‘NOSTALGIA’, each of which have as many letters between them as they have in English alphabetical series (both forward and backward direction)?

To find the pairs of letters in the word ‘NOSTALGIA’ that have the same number of letters between them as they do in the English alphabetical series (in both forward and backward directions), we can analyze the word step-by-step.

First, let us write down the word and the position of each letter in the English alphabetical order:
N = 14
O = 15
S = 19
T = 20
A = 1
L = 12
G = 7
I = 9
A = 1

Now, we check for pairs of letters by counting the alphabetical distance between them in both directions:

1. Forward Direction:
- From N (14) to O (15): There are 0 letters between them in the word, and 0 letters between N and O in the alphabet. This is our first pair: (N, O).
- From S (19) to T (20): There are 0 letters between them in the word, and 0 letters between S and T in the alphabet. This is our second pair: (S, T).
- Checking other combinations forward, we do not find any more matches.

2. Backward Direction:
- Let's check starting from letters on the right towards the left:
- From G (7) to I (9) backward (i.e., looking at the sequence I - A - G in the word): The letters are G (7) and I (9). In the alphabet, G and I have 1 letter (H) between them. In the word ‘NOSTALGIA’, G and I have exactly 1 letter (A) between them. This is our third pair: (G, I).
- Checking other combinations backward, we do not find any more matches.

Thus, there are exactly three such pairs: (N, O), (S, T), and (G, I).

Therefore, the correct option is Three.