In order to determine the polarity of an unmarked horse shoe magnet, you have several options to consider.

Option 1: Using a charged glass rod - This option is not relevant for determining the polarity of a magnet. A charged glass rod will not provide any information about the orientation of the magnet`s poles.

Option 2: Using a magnetic compass - This is the correct option. A magnetic compass can be used to determine the polarity of a magnet. By placing the compass near the magnet, the needle of the compass will align with the magnetic field lines of the magnet. This alignment will indicate the orientation of the poles of the magnet, allowing you to determine its polarity.

Option 3: Using an electroscope - This option is not relevant for determining the polarity of a magnet. An electroscope is used to detect the presence of electric charges, not magnetic fields.

Option 4: Using another unmarked bar magnet - While it is possible to use another magnet to determine the polarity of a magnet, it may not be the most accurate or reliable method. In this case, a magnetic compass is a better choice as it directly indicates the orientation of the poles.

In conclusion, the correct option for determining the polarity of an unmarked horse shoe magnet is option 2, using