In their chemical behaviour, the earlier members of the lanthanoid series are quite reactive, similar to X, but with increasing atomic number they behave more like Y. Which of the following correctly identifies X and Y?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → X = Calcium, Y = Aluminium
The earlier lanthanoids are quite reactive, like the alkaline earth metal calcium. As the atomic number increases along the series, they become more like aluminium in their chemical behaviour.
NCERT (2026-27 edition):
4.5.4 General Characteristics – “In their chemical behaviour, in general, the earlier members of the series are quite reactive similar to calcium but, with increasing atomic number, they behave more like aluminium.”