Step 1: Understand the sentence.
The sentence specifies the day on which the meeting is planned to take place.
Step 2: Recall the correct usage.
The expression
\[
\boxed{\text{scheduled for}}
\]
is the standard and grammatically correct collocation used to indicate the planned date or time of an event.
Step 3: Analyse the options.
• (A) in -- Incorrect. It is generally used for months, years, or longer periods.
• (B) for -- Correct. "Scheduled for" is the correct expression.
• (C) at -- Incorrect. It is mainly used for specific clock times.
• (D) about -- Incorrect. It does not fit the sentence.
Step 4: Final conclusion.
\[
\boxed{\text{The meeting has been scheduled for next Monday.}}
\]
Hence, the correct option is \(\boxed{(B)}\).