What is the ration of H2O:O2? 2H2 + O2 → 2H 20

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How do you identify the anode on a power source such as a battery? how do you identify the cathode? how are terms anion and cation?

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?