Question

Which of the following change(s) does the $d$ and $f$ block metals undergo when they form metallic hydrides?

• A. Decrease in density
• B. Loss of electrical conductivity
• C. Irregular lattice
• D. Law of constant proportion is not applicable

Answer 1

Answer: (A), (C), (D)

Law of constant proportion is not applicable

Metallic hydrides are formed by heating $d/f$ block metals due to which their lattice expands to provide holes for hydrogen to occupy. Hence their density decreases and they attain brittle nature.
The holes formed in this process can be occupied by any of hydride ions or hydrogen atoms or hydrogen ions with delocalised electrons. Due to this irregularity, metallic hydrides conduct electricity and exihibit irregular lattice. They also defy law of constant proportion.