Derive an expression for the angular frequency of small oscillation of the bob of a simple pendulum when it is immerased in a liquid of density `rho`. Assume the density of the bob as `sigma` and length of the string as `l`.

Explanation

To derive the expression for the angular frequency of small oscillations of the bob of a simple pendulum when immersed in a liquid, we can follow these steps:

### Step 1: Identify the Forces Acting on the Bob
When the bob is immersed in a liquid, two main forces act on it:
1. The gravitational force (weight) acting downward, given by \( F_g = mg \), where \( m \) is the mass of the bob.
2. The buoyant force acting upward, given by \( F_b = \rho V g \), where \( \rho \) is the density of the liquid and \( V \) is the volume of the bob.

### Step 2: Express the Mass of the Bob
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