Read the following paragraph and answer the questions given below ,
Stable equilibrium is of various type . Mechanical equilibrium is achieved when all particles are at rest and total potential energy of the system is minimum . At any stage where particles are at rest but the system is not at stabel equilibrium as it can reduce its potential energy by reverting to another position, is called metastable equilibrium . Thermal equilibrium is result from the absence of temperature gradients in the system. chemical equilibrium is obtained when no further reaction occurs between reacting substances, i.e forward and reverse rates of reaction are equal. when steam with solid iron at high temperature `Fe_3O_4(s)` and hydrogen gas are produced . But the reaction never goes to completion. this is because as the products are formed the reaction proceeds in reverse direction and when rate of reverse reaction is equal to rate of forward reaction , the concentration of reactants and products become constant and equilibrium is reached.
When a matchbox is balanced on its edge, it is unstable and will tumble to a more stable position resting on its face so as to acquire minimum potential energy. This is an example of

Options

A. chemical equilibrium
B. thermodynamic equilibrium
C. mechanical equilibrium
D. change of metastable state to mechanical equilibrium state

Answer

To solve the question based on the provided paragraph, we will analyze the information given and identify the type of equilibrium described in the scenario of a matchbox balanced on its edge.

### Step-by-Step Solution:

1. **Understanding the Types of Equilibrium**:
- The paragraph describes various types of equilibrium: mechanical, metastable, thermal, and chemical equilibrium.
- Mechanical equilibrium occurs when all particles are at rest and the total potential energy of the system is at a minimum.

2. **Identifying the Scenario**:
- The scenario presented is about a matchbox balanced on its edge.
- This situation implies that the matchbox is in a position that is not stable, as it can easily fall over to a more stable position.

3. **Analyzing Stability**:
- When the matchbox is balanced on its edge, it is in an unstable equilibrium. This means that while the matchbox is at rest, it has the potential to move to a lower energy state (resting on its face), which is more stable.
- The matchbox will tumble to a position where it has a larger base of support (resting on its face), thus acquiring minimum potential energy.

4. **Conclusion**:
- Since the matchbox is initially balanced on its edge (unstable equilibrium) and can move to a more stable position (resting on its face), this situation exemplifies **Mechanical Equilibrium**.

### Final Answer:
The example of a matchbox balanced on its edge is an example of **Mechanical Equilibrium**.

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