Choose the correct preposition to fill in the blank:

The Rajdhani Express is due to arrive _____ platform No. 3.

at

The correct answer is Option (4) → at

• In is typically used for enclosed spaces or concepts. ("in the box," "in love").
• Into suggests movement towards the inside of something. ("He jumped into the pool").
• At is used for specific locations or points in time. ("The meeting is at 3 PM," "The train is at the station").

Since the train is arriving at a specific location (platform No. 3), "at" is the most appropriate preposition.