A solution that has the highest boiling point among the following is -

1. 1.0 M NaOH

2. 1.0 M Na2SO4 

3. 1.0 M NH4NO3

4. 1.0 M KNO3

Hint: Boiling point of solution directly proportional to the van't Hoff factor value

Explanation:

As we know greater the value of van't Hoff factor higher will be the elevation in boiling point and hence higher will be the boiling point of the solution. The values are as follows:

Solution

van't Hoff factor (i)

1.0 M NaOH

1.0 M Na2SO4 

1.0 M NH4NO3 

1.0 M KNO3

2

3

2

2

Hence, 1.0 M Na2SO4 has the highest value of the boiling point.