Question

Identify the incorrect statement:

• A. Activity of an ideal gas is equal to its partial pressure and is unity
• B. Activity of non-ideal gas is equal to its fugacity and is unity
• C. Activity of pure solid and liquid in standard state is unity
• D. Activity is ratio of fugacity in actual state to standard state fugacity

Hint:

Activity is always dimensionless and defined as a ratio, not an absolute value.

Answer 1

The Correct Option is B

Concept: Activity is defined as: \[ a = \frac{f}{f^\circ} \] where: - $f$ = fugacity of substance in actual state - $f^\circ$ = fugacity in standard state For ideal gases: \[ f = P \Rightarrow a = \frac{P}{P^\circ} \]

Step 1: Check statement (A).
For ideal gases: \[ a = \frac{P}{P^\circ} \] If $P^\circ = 1$ bar: \[ a = P \] So statement is acceptable in standard convention.

Step 2: Check statement (B).
For non-ideal gases: \[ a = \frac{f}{f^\circ} \] Activity is NOT equal to fugacity itself. It is a ratio. Also activity is not always unity unless at standard state. Hence statement (B) is incorrect.

Step 3: Check (C).
For pure solids and liquids in standard state: \[ a = 1 \] So correct.

Step 4: Check (D).
This matches definition exactly: \[ a = \frac{f}{f^\circ} \] So correct. Final Answer: \[ \boxed{\text{(B)}} \]