A: the characteristics of cathode rays do not depend upon the material of electrodes and the nature of gas present in the cathode ray tube.
R: cathode rays consist of negatively charged particles, called electrons.

Explanation:

The given assertion and reason both relate to the characteristics of cathode rays. Let's discuss each statement individually and then analyze how the reason provides a correct explanation for the assertion.

Assertion: The characteristics of cathode rays do not depend upon the material of electrodes and the nature of gas present in the cathode ray tube.

The assertion states that the characteristics of cathode rays remain unaffected by the material of electrodes and the nature of gas present in the cathode ray tube. In other words, regardless of the materials used for the electrodes or the type of gas present, cathode rays possess the same properties.

Reason: Cathode rays consist of negatively charged particles, called electrons.

The reason provided for the assertion states that cathode rays are composed of negatively charged particles known as electrons. This is a well-established fact in physics.

Explanation:

The reason correctly explains the assertion because the characteristics of cathode rays are primarily determined by the properties of the electrons. The material of the electrodes and the nature of the gas do not have a significant influence on the behavior of the electrons within the cathode ray tube.

Here's a detailed explanation of why the reason is a correct explanation for the assertion:

1. The production of cathode rays: Cathode rays are generated when a high voltage is applied across the electrodes in a vacuum tube. When the voltage is applied, electrons are emitted from the cathode (negative electrode) and accelerated towards the anode (positive electrode).

2. Nature of cathode rays: The properties of cathode rays, such as their ability to be deflected by electric and magnetic fields, their fluorescence, and their heating effect, are all due to the behavior of the electrons. The electrons in the cathode rays carry negative charge and exhibit particle-like behavior.

3. Independence of material and gas: The material of the electrodes and the nature of the gas inside the cathode ray tube do not affect the fundamental properties of the electrons. The electrons will behave in a similar manner regardless of the material used for the electrodes or the gas present.

4. Electron behavior: The behavior of electrons is governed by fundamental principles of physics, such as electric and magnetic forces. These principles are independent of the specific materials used for the electrodes or the gas present in the tube.

In conclusion, the reason provided is a correct explanation for the given assertion. The characteristics of cathode rays do not depend on the material of electrodes or the nature of the gas because the properties of cathode rays are mainly determined by the behavior of the electrons, which remain consistent regardless of these factors.