Confusing into and in to is a very common mistake.
1. Into is a preposition that describes movement towards or inside something.
- The train disappeared into the tunnel.
- I think he went into that shop.
- Plug the mouse into the computer.
2. In to is an adverb (in) followed by a preposition (to). They often sit together due to correct sentence construction.
- I will hand this bag full of money in to the police.
- The courier came in to deliver a parcel.
Note: These sentences work without the adverb in. The adverb makes the sentences more expressive and definite.
- I will hand this bag full of money to the police.
- The courier came to deliver a parcel.
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