basic beryllium fluoride
21Niobium — zirconium ← niobium → molybdenum V ↑ Nb ↓ Ta …
22Cerium — lanthanum ← cerium → praseodymium ↑ Ce ↓ Th …
23Radon — This article is about the chemical element. For other uses, see Radon (disambiguation). astatine ← radon → francium Xe ↑ Rn ↓ Uuo …
24ion-exchange reaction — ▪ chemical reaction Introduction any of a class of chemical reactions between two substances (each consisting of positively and negatively charged species called ions (ion)) that involves an exchange of one or more ionic components.… …
25Africa — /af ri keuh/, n. 1. a continent S of Europe and between the Atlantic and Indian oceans. 551,000,000; ab. 11,700,000 sq. mi. (30,303,000 sq. km). adj. 2. African. * * * I Second largest continent on Earth. It is bounded by the Mediterranean Sea,… …
26Neodymium — praseodymium ← neodymium → promethium ↑ Nd ↓ U …
27Phosphorus — This article is about the chemical element. For other uses, see Phosphorus (disambiguation). silicon ← phosphorus → sulfur …
28Lead poisoning — Classification and external resources An X ray demonstrating the characteristic finding of lead poisoning, dense metaphyseal lines. ICD 10 T …
29Lighter than air — Some gases are buoyant in air because they have densities lower than that of air (about 1.2 kg/m3, 1.2 g/l). Lighter than air gases are used to fill craft called aerostats, which include free balloons, moored balloons, and airships, to make the… …
30luminescence — luminescent, adj. /looh meuh nes euhns/, n. 1. the emission of light not caused by incandescence and occurring at a temperature below that of incandescent bodies. 2. the light produced by such an emission. [1885 90; < L lumin (see LUMEN) +… …
