A 20.9 mL sample of a solution of RbOH is neutralized by 21.39 mL of a 2.548 M solution
of HBr. What is the molarity of the RLOH
solution?
Answer in units of M.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)