Help, please...I have no idea what I'm doing :D

An electron moved from shell n = 2 to shell n = 1. what most likely happened during the transition? a fraction of a photon was added. a photon of energy was absorbed. a fraction of a photon was removed. a photon of energy was released.

Although respiratory organs vary across different organisms, they all contain respiratory surfaces that have a large surface area and are extremely thin. explain why having an extremely thin respiratory surface with a large surface area is advantageous for the process of gas exchange

What are the advantages of using the metric system? designed as a decimal system making conversions simpler more accurate system of measurement has prefixes that correspond to an amount to use with all base units used by the entire scientific community