HELP ASAPPP An iron nail was placed in an open test tube containing some salt solution, and then left for a week for observations. The experimental setup and observations are shown below.

Which of the following best demonstrates that a chemical change has taken place?

The salt solution was discolored after a week.

The volume of the salt solution has decreased.

The mass of the salt solution, beaker and nails decreased.

The iron nail is still undissolved in the solution after a week.

Achemistry student needs to standardize a fresh solution of sodium hydroxide. he carefully weighs out of oxalic acid , a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in of distilled water. the student then titrates the oxalic acid solution with his sodium hydroxide solution. when the titration reaches the equivalence point, the student finds he has used of sodium hydroxide solution.calculate the molarity of the student's sodium hydroxide solution. be sure your answer has the correct number of significant digits.