A charge particle projected towards east is deflected towards north by a magnetic field. What is the direction of the magnetic field?

This is the correct answer. According to Fleming's left hand rule: Hold out your left hand with forefinger, middle finger and thumb at right angle to one another. If the fore finger represents the direction of the field and the middle finger represents the direction of the current, then thumb gives the direction of the force. In this case, the direction of the charge particle is towards east, i.e. the direction of the current repesented by the fore finger and the thumb repesents the direction of the force. The fore finger represents the direction of the magnetic field.