Find the mistake in one-step equations

Marcus tried to solve an equation step by step. $\qquad\begin{align} 2.5b&=5\\\\ \\ \dfrac{2.5b}{2.5}&=\dfrac{5}{2.5}&\green{\text{Step } 1}\\\\ \\ b&=3&\blue{\text{Step } 2}\\\\ \end{align}$ **Find Marcus's mistake.** [[☃ radio 1]]