As of now, the nuclear fission is the most feasible energy source for human use. All the nuclear power plants are based on the controlled nuclear fission reaction, where the unstable nucleus is bombarded with high speed neutrons, thus, splitting the nucleus into stable ones and releasing huge amount of energy. The nuclear fusion requires very high temperature, the temperature equal's to that of the sun. Hence, it is not feasible right now. As the technology advances, we will see advancement in other form of energies.
Roman numerals are used in naming ionic compounds when the metal cation forms more than one ion. The metals that form more than one ion are the transition metals, although not all of them do this.
SnBr2 - Tin(II) Bromide
2Cu + S = Cu₂S
S⁰ + 2e⁻ = S⁻²
Cu⁰ - 1e⁻ = Cu⁺¹
A sulfur atom gains two electrons.