Question

Which of the following element belongs to the third transition series of the periodic table?

• A. Sc
• B. Re
• C. Rh
• D. Tc

Answer 1

The correct option is B Re

The third transition series or 5d series corresponding to the filling of 5d sublevel consists of the following 10 elements of the $6^{th}$period: La (Atomic No.=57); Hf (Atomic No.= 72), Ta, W, Re, Os, Ir, Pt, Au and Hg (Atomic No.=80). Hence Re belongs to third transition series.