The ph of acid rain would be greater than 7 less than 7 exactly 7 exactly 14

Less than 7.

Explanation:

pH scale in chemistry is used to measure the concentration of hydrogen ion. In other words, it is used to measure the extent of acidity or alkalinity of any solution. The pH scale having numbers that range from 0 to 14. The acidic solution has a lower pH value while the basic solution has a higher pH. The pH value of pure water is 7.

As the name implies acid rain, it is formed by the combination of sulfur and nitrogen oxides. The pH of acid rain is less than 7. Typically its value is 4.  

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask