Question

Stability index, determined for evaluating the stability of oil–water viscous emulsions, based on electric conductivity changes during non‐destructive short heating–cooling–heating cycles,
A. is defined as \(\frac{Δ}{h}\), where h is the change in the conductivity between 35°C and 45°C and Δ is the conductivity interval within the two heating curves at 35°C 
B. indicates the relative change in enthalpy between two cycles 
C. is defined as \(\frac{2Δ}{h}\), where h is the change in the conductivity between 35°C and 45°C and Δ is the conductivity interval within the two heating curves at 35°C 
D. indicates the relative change in conductivity between two cycles 
Choose the correct answer from the options given below:

• A. A and B only
• B. B and C only
• C. C and D only
• D. D and A only

Answer 1

The Correct Option is D

To determine the correct answer, we need to analyze the components of the provided question and identify which options accurately describe the concept of "stability index" for oil-water viscous emulsions. 

The "stability index" in this context is related to the electrical conductivity changes during non-destructive short heating-cooling-heating cycles, a method used to study the stability of emulsions. Let's evaluate each statement given in the options:

1. Option A: \(\frac{Δ}{h}\), where \(h\) is the change in the conductivity between 35°C and 45°C and \(Δ\) is the conductivity interval within the two heating curves at 35°C.

This definition aligns with the method of measuring stability, as the ratio of change in conductivity (\(Δ\)) relative to a particular conductivity change point (\(h\)) between two heating curves. It accurately describes a stability index used in this experimental context.

1. Option B: Indicates the relative change in enthalpy between two cycles.

This statement is incorrect, as the stability index described is related to conductivity changes, not enthalpy changes.

1. Option C: \(\frac{2Δ}{h}\), where \(h\) is the change in the conductivity between 35°C and 45°C and \(Δ\) is the conductivity interval within the two heating curves at 35°C.

This statement is incorrect because it introduces an incorrect factor of 2 in the formula, which is not standard for calculating the stability index mentioned here.

1. Option D: Indicates the relative change in conductivity between two cycles.

This is a correct statement as it refers to the relative change in conductivity, reflecting the logical evaluation of emulsion stability across cycles.

Based on the above analysis, the options that correctly describe the stability index based on conductivity changes are statements in options A and D. Therefore, the correct choice is:

D and A only.