State the postulate of Bohr.s theory regarding :
(1) Angular momentum of an electron.
(2) Emission of a photon.
(ii) Total energy of an electron orbiting around the nucleus of an atom is always negative. What is the significance of this?

Explanation

### Step-by-Step Solution

**(1) Angular Momentum of an Electron:**
According to Bohr's third postulate, the angular momentum (L) of an electron in a stable orbit around the nucleus is quantized and is given by the formula:
\[ L = mvr = n \frac{h}{2\pi} \]
where:
- \( m \) is the mass of the electron,
- \( v \) is the velocity of the electron,
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