Is the reaction exothermic or endothermic

The graph shows that the temperature of the solution decreases after the reaction starts (around $t = 2\frac{1}{2}$ minutes). The calculated $\Delta T$ is $-0.8^\circ\text{C}$, indicating a drop in temperature.

An endothermic reaction absorbs heat from its surroundings, causing the temperature of the surroundings (in this case, the solution) to decrease. Conversely, an exothermic reaction releases heat, causing the temperature to increase.

Since the temperature of the solution decreased, the reaction absorbed heat from the surroundings. Therefore, the reaction is endothermic.