Statement I states that it is not necessary for every bar magnet to have one North Pole and one South Pole. This means that there could be bar magnets that do not have this characteristic.

Statement II states that magnetic poles occur in pairs. This means that for every North Pole, there is a corresponding South Pole and vice versa.

Option 4 states that Statement I is false but Statement II is true. This means that it is incorrect to say that every bar magnet has one North Pole and one South Pole (Statement I), but it is true that magnetic poles occur in pairs (Statement II).

In other words, while it is common for bar magnets to have one North Pole and one South Pole, there can be exceptions where this is not the case. However, it is always true that magnetic poles come in pairs, meaning that if one pole exists, there must be a corresponding opposite pole.

Therefore, option 4 is the correct answer.