1. We evaluate each statement about equilibrium in physical processes.

2. Statement (A):

Equilibrium is possible only in a closed system at a given temperature.

This is correct.

For a system to attain equilibrium, matter should not escape from the system; otherwise the forward and reverse processes cannot balance properly. Also, equilibrium is defined at a fixed temperature.

So, (A) is correct.

3. Statement (B):

Both the opposing processes occur at the same rate.

This is the defining condition of dynamic equilibrium.

If a physical process and its reverse occur at equal rates, there is no net macroscopic change.

So, (B) is correct.

4. Statement (C):

When equilibrium is attained at a given temperature, the value of all its parameters became equal.

This is incorrect.

At equilibrium, macroscopic parameters such as pressure, concentration, density, etc. become constant with time, not necessarily equal to one another.

For example, in liquid-vapour equilibrium, vapour pressure becomes constant, but it is not “equal” to all other parameters.

So, (C) is incorrect.

5. Statement (D):

For dissolution of solids in liquids, the solubility is constant at a given temperature.

This is correct.

For a given solid-solvent system, solubility has a fixed value at a fixed temperature (assuming pressure effects are negligible for solids in liquids).

So, (D) is correct.

6. Count the correct statements

Correct statements are:

• (A)
• (B)
• (D)

Hence, total number of correct statements is

$3$

7. Comparison with stored answer

Stored correct answer = $3$

Our derived answer = $3$

Hence, the answer agrees with the stored answer.