In this scenario, a positively charged particle is moving towards the west and gets deflected towards the north. This deflection is caused by a magnetic field. According to the right-hand rule for the force on a moving charged particle, when the particle`s velocity is directed towards the west and the force on it is directed towards the north, the magnetic field must be directed towards the upward direction.
To better understand this, let`s visualize it. Imagine you are holding your right hand such that your palm is facing downwards, and your thumb is pointing towards the west (representing the direction of the particle`s velocity). If you extend your fingers, they would be pointing towards the north (representing the direction of the force on the particle). According to the right-hand rule, the magnetic field is then directed upwards, perpendicular to both the velocity and force vectors.
Option 4 correctly states that the direction of the magnetic field is upwards, which is the correct explanation for the deflection of the positively charged particle towards the north.