Answer 1

The van’t Hoff factor is defined as the ratio of observed colligative property produced by a given concentration of electrolyte solution to the property observed for the same concentration of non-electrolyte solution.

Van't Hoff factor : 
To account for the extent of dissociation or association, van’t Hoff introduced a factor i , known as the van’t Hoff factor.

`i = "Observed colligative property of electrolyte solution"/"Observed colligative property of non-electrolyte solution of same concentration"`

It is related to the degree of dissociation as,

`a = "i - 1"/"n’ - 1"`

Value of i :
For association, i < 1
For dissociation, i > 1
No association or dissociation, i = 1