Question

Among the following statement(s), what is true about colloids?
(A) They do not settle down when left undisturbed
(B) They are not visible to the naked eyes
(C) Their size generally ranges between \(10^{-5}\) and \(10^{-7}\) cm
(D) A colloidal solution is homogeneous in nature
Choose the correct answer from the options given below:

• A. (A) and (B) only.
• B. (A), (B) and (C) only.
• C. (B), (C) and (D).
• D. (A), (C) and (D) only.

Hint:

- True Solutions: Homogeneous, particle size < 1 nm (\(10^{-7}\) cm).
- Colloidal Solutions: Heterogeneous, particle size 1 nm to 1000 nm (\(10^{-7}\) to \(10^{-4}\) cm).
- Suspensions: Heterogeneous, particle size > 1000 nm (\(10^{-4}\) cm).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Colloids are mixtures in which microscopic particles of one substance (the dispersed phase) are suspended throughout another substance (the dispersion medium).
Due to their small size, colloids exhibit unique physical, optical, and kinetic properties, such as the Tyndall effect and Brownian motion.

Step 2: Detailed Explanation:
Let us analyze each statement regarding the properties of colloids:
- Statement (A): Colloidal particles are extremely small, and their constant collision with the molecules of the dispersion medium (Brownian motion) keeps them suspended.
Thus, they do not settle down under the influence of gravity when left undisturbed, making this statement true.
- Statement (B): Colloidal particles are much smaller than the resolving power of the human eye, meaning they cannot be seen with the naked eye.
They can only be observed using an ultra-microscope or electron microscope, making this statement true.
- Statement (C): The diameter of colloidal particles typically ranges from 1 nanometer (nm) to 1000 nanometers (nm).
Converting this to centimeters:
\[ 1\text{ nm} = 10^{-7}\text{ cm} \]
\[ 100\text{ nm} = 10^{-5}\text{ cm} \]
Therefore, the size range of $10^{-5}$ to $10^{-7}$ cm (or $10^{-7}$ to $10^{-5}$ cm) falls squarely within the defined colloidal range, making this statement true.
- Statement (D): A colloidal solution is heterogeneous in nature because it consists of two distinct phases (dispersed phase and dispersion medium), even though it may appear homogeneous to the naked eye.
Thus, this statement is false.
Therefore, statements (A), (B), and (C) are true.

Step 3: Final Answer:
The correct option is (B), representing (A), (B), and (C) only.