Correct Option
The Assertion (A) states that the temperature of a metal wire rises when an electric current is passed through it. This statement is true. When an electric current flows through a conductor, the free electrons, which constitute the current, frequently collide with the fixed positive ions (atoms) of the metal lattice. These collisions impede the flow of electrons and convert a portion of the electrical energy into heat energy, causing the temperature of the wire to increase. This phenomenon is known as the Joule heating effect.
The Reason (R) states that the temperature rise is due to collisions of metal atoms with each other releasing heat energy. This statement is false. While atoms in a metal lattice vibrate, the primary mechanism for heat generation when current flows is the collision between the drifting free electrons and the vibrating positive metal ions (lattice atoms), not collisions between the metal atoms themselves in a manner that explains the heating effect of current.
Since Assertion (A) is true and Reason (R) is false, option 3 is the correct choice.
Incorrect Options
Option 1 is incorrect because Reason (R) is false.
Option 2 is incorrect because Reason (R) is false.
Option 4 is incorrect because Assertion (A) is true, not false.