<P> Indium ( / ˈɪndiəm / IN - dee - əm ) is a chemical element with the symbol In and atomic number 49 . This rare , very soft , malleable and easily fusible other metal is chemically similar to gallium and thallium , and shows the intermediate properties between these two . Indium was discovered in 1863 and named for the indigo blue line in its spectrum that was the first indication of its existence in zinc ores , as a new and unknown element . The metal was first isolated in the following year . Zinc ores continue to be the primary source of indium , where it is found in compound form . Very rarely the element can be found as grains of native ( free ) metal , but these are not of commercial importance . </P>
the atomic number of indium which belongs to 5th period is
49