The correct answer is option 3, which states that the working of safety fuses depends on the magnitude of the current and the heating effect of the current.

Option 1, which includes all four options, is incorrect. While magnetic effect and chemical effect of the current can have some influence on certain electrical components, they are not directly related to the functioning of safety fuses.

Option 2, which includes options 1, 2, and 3, is also incorrect. Again, the magnetic effect of the current and the chemical effect of the current are not relevant to the working of safety fuses.

Option 3 correctly identifies the two factors on which the working of safety fuses depends: the magnitude of the current and the heating effect of the current. Safety fuses protect electrical circuits from excessive currents that can cause damage, and they operate by melting a fuse wire when the current exceeds a certain threshold. This melting occurs due to the heating effect of the current, thereby breaking the circuit and preventing further damage.

Option 4, which states that the working of safety fuses depends only on the heating effect of the current, is incorrect. The magnitude of the current also plays a crucial role in the operation of safety fuses.

In conclusion, the correct answer