Bottles containing ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{I}$ and ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{I}$ lost their original labels. They were labelled $\mathrm{A}$ and $\mathrm{B}$ for testing. $\mathrm{A}$ and $\mathrm{B}$ were separately taken in a test tube and boiled with $\mathrm{NaOH}$ solution. The end solution in each tube was made acidic with dilute ${\mathrm{HNO}}_3$ and then some ${\mathrm{AgNO}}_3$, solution was added. Substance $\mathrm{B}$ gave a yellow precipitate. Which one of the following statements is true for this experiment?