Arrange `Ce^(3+),La^(3+), Pm^(3)` and `Yb^(3+)` in increasing order of their size -

Options

A. `La^(3+) lt Ce^(3+) lt Pm^(3+) lt Yb^(3+)`
B. `Yb^(3+) lt Pm^(3+) lt Ce^(3+) lt La^(3+)`
C. `La^(3+) = Ce^(3+) lt Pm^(3+) lt Yb^(3+)`
D. `Yb^(3+) lt Pm^(3+) lt La^(3+) lt Ce^(3+)`

Answer

B

Explanation

For tripositive ions of Lanthanoids size decrease regularly as atomic no. increase due to Lanthanoid contraction.