Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at `25^(@)C` . Identify correct one
(a)The adsorption requires activation at `25^(@)C`
(b)The adsorption is accompanied by a decrease in enthalpy
(c)The adsorption increases with increases of temperature
(d)The adsorption is irreversible

Options

A. The adsorption requires activation at `25^(@)C`
B. The adsorption is accomanied by a decrease in enthalpy
C. The adsorption increases with increases of temperature
D. The adsorption is irreversible

Explanation

To solve the question regarding the adsorption of methylene blue on activated charcoal, we will analyze each of the provided statements step by step.

### Step 1: Understand the nature of adsorption
Adsorption can be classified into two types: physical (physisorption) and chemical (chemisorption). In this case, methylene blue is being adsorbed on activated charcoal, which typically involves physical adsorption.

**Hint:** Recall the characteristics of physical adsorption and how it differs from chemical adsorption.

### Step 2: Analyze statement (a)
Statement (a) claims that "The adsorption requires activation at 25°C."
- Physical adsorption does not require activation energy. It occurs spontaneously at room temperature due to van der Waals forces. Therefore, this statement is **incorrect**.

**Hint:** Think about the energy requirements for physical vs. chemical adsorption.

### Step 3: Analyze statement (b)
Statement (b) states that "The adsorption is accompanied by a decrease in enthalpy."
- Physical adsorption is an exothermic process, meaning it releases heat and is accompanied by a decrease in enthalpy (ΔH < 0). Thus, this statement is **correct**.

**Hint:** Consider the thermodynamic principles that govern exothermic reactions.

### Step 4: Analyze statement (c)
Statement (c) claims that "The adsorption increases with increases of temperature."
- For exothermic processes, the adsorption is favored at lower temperatures. As temperature increases, the adsorption decreases. Therefore, this statement is **incorrect**.

**Hint:** Relate this to Le Chatelier's principle regarding the effect of temperature on exothermic reactions.

### Step 5: Analyze statement (d)
Statement (d) states that "The adsorption is irreversible."
- Physical adsorption is generally reversible. The adsorbate can be desorbed from the adsorbent under certain conditions. Hence, this statement is **incorrect**.

**Hint:** Recall the nature of physical adsorption and whether it can be reversed.

### Conclusion
Based on the analysis:
- Statement (a) is incorrect.
- Statement (b) is correct.
- Statement (c) is incorrect.
- Statement (d) is incorrect.

Thus, the correct answer is **(b) The adsorption is accompanied by a decrease in enthalpy.**