Explanation:

To determine how many such pairs exist in the number '6315784', we need to compare the digits and count the number of digits between each pair:

- (3, 5): In '6315784', 3 and 5 have one digit between them (1). Numerically, 3 and 5 also have one digit between them (i.e., 4).

- (1, 7): In '6315784', 1 and 7 have two digits between them (5, 8). Numerically, 1 and 7 have five numbers between them (i.e., 2, 3, 4, 5, 6).

- (5, 8): In '6315784', 5 and 8 have two digits between them (7, 4). Numerically, 5 and 8 have two numbers between them (i.e., 6, 7).

Now, let's evaluate the options:

- Option 1: One

- Option 2: Two

- Option 3: Three

- Option 4: Four

- Option 5: Five

Correct Answer: Option 2: Two