Provide descriptions and diagrams for deuterium, tritium, ortho-hydrogen, and para-hydrogen.

Here are the descriptions and diagrams for deuterium, tritium, ortho-hydrogen, and para-hydrogen:

• Deuterium ($^2\text{H}$ or D) Deuterium is an isotope of hydrogen. Its nucleus contains one proton and one neutron, unlike common hydrogen ($^1\text{H}$) which has only one proton. It is also known as "heavy hydrogen."

  $$\boxed{\text{Diagram of Deuterium}}$$ $$\text{p}^+ \text{ (proton)}$$ $$\text{n}^0 \text{ (neutron)}$$ $$\text{e}^- \text{ (electron)}$$ $$\text{Nucleus: } \begin{array}{|c|} \hline \text{p}^+ \\ \text{n}^0 \\ \hline \end{array} \quad \text{Orbiting: } \text{e}^-$$

• Tritium ($^3\text{H}$ or T) Tritium is another isotope of hydrogen. Its nucleus contains one proton and two neutrons. It is radioactive with a half-life of about 12.3 years.

  $$\boxed{\text{Diagram of Tritium}}$$ $$\text{p}^+ \text{ (proton)}$$ $$\text{n}^0 \text{ (neutron)}$$ $$\text{e}^- \text{ (electron)}$$ $$\text{Nucleus: } \begin{array}{|c|} \hline \text{p}^+ \\ \text{n}^0 \\ \text{n}^0 \\ \hline \end{array} \quad \text{Orbiting: } \text{e}^-$$

• Ortho-hydrogen Ortho-hydrogen is a spin isomer of molecular hydrogen (H$_2$). In ortho-hydrogen, the nuclear spins of the two hydrogen atoms (protons) are parallel to each other. This means their spins are aligned in the same direction.

  $$\boxed{\text{Diagram of Ortho-hydrogen}}$$ $$\text{H} \quad \text{H}$$ $$\uparrow \quad \uparrow \quad \text{(Parallel nuclear spins)}$$

• Para-hydrogen Para-hydrogen is another spin isomer of molecular hydrogen (H$_2$). In para-hydrogen, the nuclear spins of the two hydrogen atoms (protons) are anti-parallel to each other. This means their spins are aligned in opposite directions.

  $$\boxed{\text{Diagram of Para-hydrogen}}$$ $$\text{H} \quad \text{H}$$ $$\uparrow \quad \downarrow \quad \text{(Anti-parallel nuclear spins)}$$