Question

Question No. 11
• Which among the following are twin
elements?
Answer
A. Cr-Cu
B.Ni-Co
C. Hf-Zr
D. Na-K​

Answer 1

Answer for this question is c)Hr-Zr

Answer 2

$Zr -Hf$ are twin elements. (Option C)

• Chemical twins are the elements that have the same chemical properties which can be due to their same atomic radii.
• Usually they are $d-block$ elements lying in periods 5 and 6 or $5d$ and $6d$ series.
• Since the atomic size of  $Zr-Hf$ is the same, they are said to be twin elements.
• They are twin due to lanthanoid contraction.