Complete the chemical formula for each ionic compound. Consult the periodic table to help you answer the question. Please help, currently taking my test

Write the chemical formula for a compound that is made of an element from group 1 and an element from group 17

The arrangement of particles is most ordered in a sample of

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?