Reactions that undergo shifts in their equilibrium must be... A. reversible reactions
B. chemical reactions
C. physical reactions
D. nuclear reactions

A. Reversible reactions.

Explanation:

Reactions that undergo shifts in their equilibrium must be reversible reactions.

A reversible reaction is a chemical reaction that is capable of forming it's reactants back from the resulting formation of products. This simply means that, reversible reactions are chemical reactions that are in equilibrium because the forward and reverse path happens at the same rate.

For example, the reaction of hydrogen gas and iodine gas to form a chemical compound called hydrogen Iodide is a reversible chemical reaction.

Forward reaction:

Reverse reaction:

A reversible reaction is denoted with a double arrow.

Also, reversible chemical reactions are controlled by the Le Chatelier's principle.

it means there are 3 atoms of oxygen

hurricanes form when warm, moist air from the ocean surface quickly rises into the atmosphere and forms storm clouds and rain. when the clouds are formed, heat is released which warms the cool air in the upper regions of the atmosphere so that the cycle can continue. which two phases of the water cycle are repeated in this process?