To answer this question, you need to understand the different processes involved in encryption.
Option A) Transposition - This option is incorrect because transposition is the process of rearranging the order of characters in a message or text, without changing the characters themselves.
Option B) Subtraction - This option is incorrect because subtraction is a mathematical operation and is not typically used in the process of replacing characters in an encryption key.
Option C) Substitution - This option is correct. Substitution is the process of replacing some characters with others in an encryption key. In encryption, each character in the plaintext is replaced with another character according to a predefined set of rules or mappings.
Option D) Transrelation - This option is incorrect because transrelation is not a recognized process in the field of encryption.
The correct answer is C) Substitution. This option is correct because substitution is the process of replacing some characters with others in an encryption key.