Final answer:
A magnet would affect a compass's accuracy as it can produce a magnetic field that could interfere with the alignment of the compass needle with the Earth's magnetic field. Therefore, the correct answer is 1) A magnet.
Step-by-step explanation:
An example of an item that, when placed near a compass, would affect its accuracy is a magnet. A compass is a navigational instrument designed to align itself with the Earth's magnetic field.
When another magnetic field, such as that from a bar magnet, is in close proximity, the compass needle will respond to it rather than to the Earth's magnetic field.
This occurs because the compass needle is itself a small magnet whereas items like rulers, pencils, and most calculators do not typically possess a strong enough magnetic field to interfere with a compass needle's orientation.
When a magnet is placed near a compass, it can interfere with the compass needle's ability to align with Earth's magnetic field, causing the needle to point in the wrong direction.