Question

Limiting compositions of f-block hydrides are
A. \[M{H_2}\mid andM{H_3}\mid \]
B. \[M{H_3}\mid andM{H_5}\mid \]
C. \[M{H_2}\mid andM{H_8}\mid \]
D. \[M{H_2}andM{H_6}\mid \]

Answer 1

Hint: Before we proceed into the problem, it is important to know the definition of f-block elements. The last electron of an F block element enters the anti-penultimate shell, which is inner to the penultimate shell where the last electron of a d-block element enters. Lanthanides are referred to as f-block elements because the final electron is filled into the orbital. "n-2" fills the f orbitals of the electron shell. The f orbitals can only hold a maximum of fourteen electrons.

Complete Step by Step Answer:
There is room for fourteen f-block elements in periods starting with the sixth. Although these components are typically not categorised, group 3 is where some authors place them.
We are asked to determine the limiting composition of -block hydrides.
With exception of d block elements (transition elements), f block elements create hydrides with fixed \[M{H_2}\] or \[M{H_3}\] compositions.

However, d block elements will create non-stoichiometric hydrides in the absence of a specified composition.

The composition of hydrides varies with temperature and pressure, among other factors.
But both d block element hydrides and f-block elements hydrides are intermittent hydrides.
The hydrogen will be wrapped between the metal atom gaps.
Therefore, limiting compositions of f-block hydrides are \[M{H_2}\mid andM{H_3}\mid \]
Hence, the option A is correct

Note: The inner layer present in the periodic table is occupied with the d block elements. The inner d orbits of groups \[3-13\] are gradually filled. On the flip side, the f block elements are found beyond and at the bottom of the periodic table. So, one should be thorough with periodic tables in order to answer these types of questions.