Which one of the given elements shows the maximum number of different oxidation states in its compounds? 

Am or Americium is a synthetic radioactive chemical element having atomic number 95. It is one of the member of the actinide series.

It is a relatively soft radioactive metal with a silvery appearance. Mostly its oxidation is +3 in chemical compounds. It has various other oxidation states ranging from +2 to +7.

Am has the greatest variety of oxidation states. Am can exist in the oxidation states +3, +4, +5, and +6. The +3 oxidation state is seen in La, Gd, and Fm.

Hence option (A) is correct.