Given question is:
Given a food with a relative humidity of 81%, what is the water activity in that food?
Explanation:
Water activity in food can be determined by using the below-shown formula:
[tex]water activity=\frac{equilibrium relative humidity}{100}[/tex]
Equilibrium is established between the vapor pressure of food and the surrounding air media.
Thus, for the given food the relative humidity is 81%.
hence, its water activity is
[tex]81/100\\=0.81[/tex]
