1. The problem states that two elements A and B are from the 1st transition series (elements with 3d electrons). 2. Element A forms an intermetallic alloy with aluminum and its maximum oxidation state does not exceed its group number. 3. The 1st transition series includes elements from Scandium (Sc, atomic number 21) to Zinc (Zn, atomic number 30). 4. The maximum oxidation state of an element in the 1st transition series usually equals its group number (3 to 12). 5. Since element A's maximum oxidation state does not exceed its group number, it suggests element A is an early transition metal with typical oxidation states. 6. Element B also forms an intermetallic alloy with aluminum, and we need to find the number of single electrons in its 3d sublevel. 7. The number of single electrons in the 3d sublevel corresponds to the number of unpaired electrons in the 3d orbitals. 8. The options given are 0, 1, 2, or 3 single electrons. 9. Considering the 1st transition series and typical electron configurations: - Sc (3d1 4s2) has 1 unpaired electron. - Ti (3d2 4s2) has 2 unpaired electrons. - V (3d3 4s2) has 3 unpaired electrons. - Cr (3d5 4s1) has 5 unpaired electrons. - Mn (3d5 4s2) has 5 unpaired electrons. - Fe (3d6 4s2) has 4 unpaired electrons. - Co (3d7 4s2) has 3 unpaired electrons. - Ni (3d8 4s2) has 2 unpaired electrons. - Cu (3d10 4s1) has 1 unpaired electron. - Zn (3d10 4s2) has 0 unpaired electrons. 10. Since element A's maximum oxidation state does not exceed its group number, element A is likely an early transition metal (Sc, Ti, or V). 11. Element B is another element from the series forming an intermetallic alloy with aluminum. 12. The question asks for the number of single electrons in the 3d sublevel of element B. 13. The best match for element B with the given options is Ni (3d8 4s2) with 2 unpaired electrons. Final answer: 2 Therefore, the number of single electrons in the 3d sublevel of element B is 2.