Why does the solution turn from yellow to blue?

Bromothymol blue (BMB) is an indicator dye that turns yellow in the presence of acid. When carbon dioxide is added to the solution, it creates carbonic acid, lowering the pH of the solution. BMB is blue when the pH is greater than 7.6, green when the pH is between 6-7.6, and yellow when the pH is less than 6.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).