The question Statement (Assertion) and Statement (Reason). The question has choices (a), (b), (c) and (d) out of which ONLY ONE is correct. So, select the correct choice.
Choices are
Statement : Magnetic field lines are closed curves.
Statement : Magnetic monopoles can't exist.
Statement is True, Statement is True; Statement is a correct explanation for Statement
Explanation for Assertion statement:
Magnetic field lines are closed curves that emerge from the North pole of the magnet and enter the South pole, i.e. field lines outside the magnet run north to south, and field lines inside the magnet go south to north.
Explanation for Reason statement:
Statement is True, Statement is True; Statement is a correct explanation for Statement .
Hence, option (a) is correct.