Why are some elements radioactive? Why are rubies red? Which element is used in sky writing? Find out the answers to these and other fascinating questions in ‘Tungsten and the Elements of Groups 3 to 7’. These elements are also called transition metals. Some occur naturally, and others are manufactured. They include chromium, molybdenum, manganese, scandium, yttrium, lanthanum, actinium, titanium, zirconium, hafnium, vanadium, and niobium.