The chemical symbol of barium is:

An element's chemical symbol typically consists of two characters. Every chemical symbol has a capital letter for the first letter and a tiny letter for the second.

An atom or an element is represented by the chemical symbol. Usually one or two letters from the Latin alphabet—always the first one capital—make up the chemical symbol for an element. The symbols come from a variety of origins, such as the German or Greek names of elements, among others. For instance, the symbol for tungsten is W, which is taken from the German term for tungsten, Wolfram, and the sign for lead is Pb, which is derived from the Latin name for lead, plumbum.

Barium has the chemical symbol Ba. A chemical element with the atomic number 56 is called barium. The fifth element in group 2 of the periodic table, barium is a group 2 element. Alkali metal compound barium is a soft, silvery metal. Barium is very reactive, and as a result, it is never found in nature as a free element.
A symbol for an element also includes any additional information like superscripts or subscripts. It comprises the element's atomic number, mass number, and occasionally charge.

Hence, the correct option is (A).