An experiment to test the conductance of 0.1 M solutions of the substances listed below was performed.

 An experiment to test the conductance of 0.1 M solutions of the substances listed below was performed.

I ammonia

II ammonium chloride

III ethanoic acid

IV sodium ethanoate

Which pair of substances show the least conductance?

A. I and II

B. I and III

C. I and IV

D. II and III

E. II and IV

The correct answer is B. I and III

Explanation: An experiment was conducted to test the conductance of four 0.1 M solutions of different substances. The substances are 

I. ammonia, 

II. ammonium chloride, 

III. ethanoic acid, and 

IV. sodium ethanoate. 

The question asked which pair of substances exhibits the least conductance.

Conductance refers to the ability of a substance to allow an electric current to pass through it. Substances that are strong electrolytes, such as acids, bases, and salts, are good conductors of electricity. Weak electrolytes, such as weak acids and bases, partially dissociate into ions and conduct electricity to a lesser extent. Non-electrolytes, such as hydrocarbons, do not dissociate into ions and do not conduct electricity.

Out of the four substances listed, ammonia and ethanoic acid are weak bases and acids, respectively. Ammonium chloride and sodium ethanoate are salts and strong electrolytes. As weak electrolytes, ammonia and ethanoic acid do not dissociate completely into ions and conduct electricity to a lesser extent than the salts. Therefore, the pair of substances that exhibit the least conductance is ammonia and ethanoic acid, which is option B.

It is essential to understand the concept of strong and weak electrolytes when dealing with conductance. Knowing the dissociation behavior of a substance can help determine its ability to conduct electricity. 

SOURCE: NECO CHEMISTRY 2001 QUESTION 17