Concept:
A business letter is a formal written means of communication used by organizations, institutions, and individuals for professional purposes. It serves as a permanent record of communication and is widely used for official correspondence.
The question asks us to identify the option that is NOT an advantage of business letters.
Therefore, we must examine each option carefully.
Step 1: Examine Option (A).
Option (A): “It has wide reach.”
Business letters can be sent across cities, states, and countries through postal services and electronic communication systems.
Thus, they can reach a large audience.
Hence,
\[
\boxed{\text{This is an Advantage}}
\]
Step 2: Examine Option (B).
Option (B): “It can be standalone medium.”
A business letter generally contains complete information regarding the matter being communicated. The recipient can understand the message without requiring additional explanation.
Therefore,
\[
\boxed{\text{This is an Advantage}}
\]
Step 3: Examine Option (D).
Option (D): “It can be reproduced and repeated.”
Business letters can be photocopied, printed, archived, scanned, and shared with multiple departments whenever required.
Thus,
\[
\boxed{\text{This is an Advantage}}
\]
Step 4: Examine Option (C).
Option (C): “It is not cost effective.”
This statement describes a disadvantage rather than an advantage.
In reality, business letters are generally considered economical and cost-effective forms of communication, especially when compared with meetings, travel, or extensive verbal communication.
Therefore,
\[
\boxed{\text{This is NOT an Advantage}}
\]
Step 5: Select the correct answer.
Among the given options, only Option (C) represents a disadvantage rather than an advantage.
Hence,
\[
\boxed{\text{Option (C)}}
\]
is the correct answer.
Conclusion:
Business letters have wide reach, can function independently as a communication medium, and can be reproduced whenever necessary. The statement “It is not cost effective” does not represent an advantage.
Therefore, the correct answer is:
\[
\boxed{\text{Option (C)}}
\]