What would likely happen if you were to touch the flask in which an endothermic reaction occurring

The flask would probably feel cooler than before the reaction started.

Explanation:

An endothermic reaction means that it needs heat to continue. The required heat will be taken from the flask and by touching it the reaction reactants will cause the solution contained in the flask to cool with a drop in temperature.

The reaction vessel will feel cool

Explanation:

In an endothermic reaction, heat is absorbed by the reaction system from the surrounding. The withdrawal of heat from the surrounding causes the reaction vessel to feel cool.

Hence when an endothermic reaction is going on, the reaction vessel feels cool when touched.