What is the name of the compound represented by the formula SI2BR6

Write the chemical symbols for three different atoms or atomic cations with 27 electrons. asap!

What is the percentage of hydrogen in c2h4

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?