Read the following paragraph and answer the questions given below ,

Stable equilibrium is of various types . 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 stable 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 two reactants (A) and (B) are mixed to give products (C) and (D) the concentration quotient (Q) at initial stage of the reaction

Options

A. a) is zero
B. b) decreases with time
C. is independent of time
D. d) increases with time

Answer

To solve the question regarding the concentration quotient (Q) at the initial stage of the reaction when two reactants (A) and (B) are mixed to give products (C) and (D), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Chemical Equilibrium**:
- Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products.

2. **Setting Up the Reaction**:
- Consider the reaction:
\[ aA + bB \rightleftharpoons cC + dD \]
- Here, \( a \), \( b \), \( c \), and \( d \) are the stoichiometric coefficients for the reactants and products.

3. **Initial Concentrations**:
- At the initial stage of the reaction, before any products are formed, the concentrations of products \( C \) and \( D \) are both zero.
- Let’s denote the initial concentrations of reactants \( A \) and \( B \) as \( [A]_0 \) and \( [B]_0 \).

4. **Expression for Concentration Quotient (Q)**:
- The concentration quotient \( Q \) is defined as:
\[ Q = \frac{[C]^c \cdot [D]^d}{[A]^a \cdot [B]^b} \]
- At the initial stage, since no products are formed yet, we have:
\[ [C] = 0 \quad \text{and} \quad [D] = 0 \]

5. **Calculating Q at Initial Stage**:
- Substituting the initial concentrations into the expression for \( Q \):
\[ Q = \frac{[0]^c \cdot [0]^d}{[A]_0^a \cdot [B]_0^b} = \frac{0}{[A]_0^a \cdot [B]_0^b} = 0 \]

6. **Conclusion**:
- Therefore, the concentration quotient \( Q \) at the initial stage of the reaction is 0.

### Final Answer:
The correct option is **A: 0**.

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