Let's determine the block for each element provided: (A) Cd (Cadmium) Cadmium (atomic number 48) is located in Group 12, Period 5 of the periodic table. Its electron configuration is [Kr]4d105s2. Elements in Groups 3 through 12, where the d-orbitals are being filled, are known as d-block elements. Cadmium fits this description. So, (A) Cd matches with (III) d-block. (B) Eu (Europium) Europium (atomic number 63) is a lanthanide element. Lanthanides and actinides are typically placed below the main body of the periodic table and comprise the f-block elements, where the f-orbitals are being filled. Its electron configuration is [Xe]4f76s2. So, (B) Eu matches with (I) f-block. (C) Se (Selenium) Selenium (atomic number 34) is located in Group 16, Period 4 of the periodic table. Its electron configuration is [Ar]3d104s24p4. Elements in Groups 13 through 18, where the p-orbitals are being filled, are known as p-block elements. Selenium fits this description. So, (C) Se matches with (IV) p-block. (D) Ba (Barium) Barium (atomic number 56) is located in Group 2, Period 6 of the periodic table. Its electron configuration is [Xe]6s2. Elements in Group 1 (alkali metals) and Group 2 (alkaline earth metals), where the s-orbitals are being filled, are known as sblock elements. Barium fits this description. So, (D) Ba matches with (II) s-block.