Identify the following reaction as an endothermic reaction, exothermic reaction, or both endothermic and exothermic: Dissolving NH4Cl in water to make a cold pack.

Endothermic reaction

Explanation:

Endothermic reactions are defined as the type of chemical reaction in which the system absorbs the energy from the surroundings and the temperature of the surrounding decreases while in Exothermic reactions, heat is released by the system to the surroundings and it makes the surrounding warm.

The given example is an "endothermic reaction" because the reaction between NH4Cl and water is making the surrounding cool (cold pack) due to the release of heat.

Hence, the correct answer is "endothermic reaction".

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.