Why electrons are considered as the universal constituents of matter?

Explanation

### Step-by-Step Text Solution

1. **Definition of Matter**: Begin by defining matter. Matter is anything that has mass and occupies space. It is composed of atoms, which in turn are made up of subatomic particles.

2. **Discovery of Electrons**: Electrons were discovered through experiments with discharge tubes, particularly the cathode ray tube experiment conducted by J.J. Thomson. This experiment revealed the existence of cathode rays, which were later identified as streams of electrons.

3. **Identical Nature of Electrons**: One of the key findings from the cathode ray experiments was that electrons are identical regardless of the source from which they are emitted. This means that electrons emitted from different materials or under different conditions (such as different cathodes or gases in the discharge tube) exhibit the same properties.

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