机 and 椅子: arranging desks and chairs
Describe a work surface and a seat through locations and quantities.
Things on a desk
机 (つくえ) means desk. 「机の上に本があります」 locates a book on the desk.
「机で手紙を書きました」 means writing a letter at the desk. It does not establish that writing was put directly on the desk surface.
Sitting on a chair
椅子 (いす) means chair. 「椅子に座ってください」 asks someone to sit on a chair.
「椅子を机の前に置きました」 says the chair was placed in front of the desk. The moved object is the chair.
Checking spatial relationships
「机の下に椅子を入れました」 means putting the chair under the desk. 机の下 gives the destination.
「机は一つ、椅子は二つ必要です」 specifies one desk and two chairs. Keep the quantities assigned to their respective objects.
Which item moved in 「椅子を机の前に置きました」?
Show the answer and why
The chair. The desk is the reference point for its location.