Under certain conditions, nuclei can undergo nuclear reactions to release energy.

Explain what is meant by nuclear fusion.

State one advantage and one disadvantage of generating electrical power in nuclear fission power stations compared with solar power systems.

Deuterium is an isotope of hydrogen ($H$) with 1 proton and 1 neutron. Tritium is another isotope of hydrogen with 1 proton and 2 neutrons. Nuclear fusion occurs when a nucleus of deuterium and a nucleus of tritium combine at extremely high temperatures. This reaction forms an isotope of helium ($He$) with 2 protons and 2 neutrons, and releases a single neutron.

Use nuclide notation to write down the balanced equation for this nuclear reaction.