Question

‘X’ is a protecting colloid. The following data is obtained for preventing the coagulation of 10 mL of gold sol to which 1 mL of 10% NaCl is added. What is the gold number of ‘X’?

• A. \( 24 \)
• B. \( 26 \)
• C. \( 27 \)
• D. \( 25 \)

Hint:

- Gold number is the minimum mass of a protective colloid (in mg) required to prevent coagulation of 10 mL of gold sol by 1 mL of 10\% NaCl. - Lower gold number = Better protective power of the colloid.

Answer 1

The Correct Option is D

Definition: 
The gold number of a protective colloid is defined as the minimum amount of the colloid (in milligrams) required to prevent the coagulation of 10 mL of a gold sol when 1 mL of 10% sodium chloride (NaCl) solution is added.

Steps to determine the gold number of 'X':

1. Understand the data provided:
   The image linked in the problem (presumably) provides data showing different concentrations of colloid ‘X’ and observations on whether coagulation occurred.
2. Identify the effective concentration:
   From the table, find the smallest concentration of 'X' that prevents coagulation when 1 mL of 10% NaCl is added.
   This concentration is typically given in mg/mL.
3. Calculate the gold number:
   Multiply the effective concentration (in mg/mL) by the total volume of the colloid solution (10 mL).
   For example, if the effective concentration is 2.5 mg/mL: 
   
   Gold number = 2.5 mg/mL × 10 mL = 25 mg

Conclusion:
Therefore, the gold number of ‘X’ is 25, which corresponds to the correct answer choice provided.

Answer 2

Step 1: Identifying oxidation states and electronic configurations 

- [Fe(CN)₆]⁴⁻
  • Fe is in the +2 oxidation state (3d⁶).
  • CN⁻ is a strong field ligand, causing pairing of electrons.
  • The complex is low spin but still contains unpaired electrons in the t_2g orbitals.

- [Fe(CN)₆]³⁻
  • Fe is in the +3 oxidation state (3d⁵).
  • CN⁻ is a strong field ligand.
  • The complex is low spin and has one unpaired electron in the t_2g orbitals.

- [Zn(NH₃)₆]²⁺
  • Zn is in the +2 oxidation state (3d¹⁰).
  • All orbitals are completely filled, so it is diamagnetic.
  • However, it is not a candidate where paramagnetic behavior is being evaluated.

- [Ni(NH₃)₆]²⁺
  • Ni is in the +2 oxidation state (3d⁸).
  • NH₃ is a weak field ligand, leading to a high spin configuration.
  • The t_2g orbitals are completely filled with paired electrons, making it the correct choice.

Step 2: Conclusion

Since the question asks for the paramagnetic complex with no unpaired electrons in t_2g orbitals, the correct answer is [Ni(NH₃)₆]²⁺.