Cherylanne mixes together Chemical A and Chemical B in a test tube, forming Chemical C. The mixture instantly turns cool to the touch. She then adds Chemical D, and the reaction becomes hot and explodes. What can be known about this situation? Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction. Chemicals A and B form an exothermic reaction, and chemicals C and D form an endothermic reaction. Chemicals A and C form an endothermic reaction, and chemicals B and D form an exothermic reaction. Chemicals A and B form an exothermic reaction, and chemicals B and D form an endothermic reaction.

Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction.

Explanation:

The reaction that produced chemical C is an endothermic reaction whereas, the reaction between C and D is an exothermic one.

An exothermic change is one in which heat is liberated to the surroundings. So the surrounding becomes hotter at the end of the reaction.

An endothermic reaction is a change in which heat is absorbed from the surrounding and hence the surrounding colder at the end of the change.

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"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."