The correct answer is (a) TURN.
In the given code, each letter is represented by a 3-digit number. The first digit of the number represents the position of the letter in the alphabet, starting with 1 for A and 2 for B. The second and third digits of the number represent the order of the letters in the word, starting with 1 for the first letter and 2 for the second letter.
For example, RUNG is represented by 5432 because R is the 18th letter of the alphabet, U is the 21st letter, N is the 14th letter, and G is the 7th letter.
FAST is represented by 6108 because F is the 6th letter of the alphabet, A is the 1st letter, S is the 19th letter, and T is the 20th letter.
8453 can be represented by TURN because T is the 20th letter of the alphabet, U is the 21st letter, R is the 18th letter, and N is the 14th letter.
The other options are incorrect because they do not follow the same pattern as RUNG and FAST.