Mo Molybdenum The 42nd element in the periodic table is molybdenum (Mo): a metallic element that resembles chromium and tungsten in many properties, is used especially in strengthening and hardening steel, and is a trace element in plant and animal metabolism.

Tm Thulium Thulium (Tm) has an atomic number of 69. Pure thulium metal has a bright, silvery luster, which tarnishes slowly on exposure to air and burns readily at 150 °C to become thulium oxide: 4Tm + 3O2 → 2Tm2O3. Thulium is now considered to be about as rare as silver, gold, or cadmium.

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