The correct sequence of thermal stability of the following carbonates is:

Identify the correct statements with respect to compounds of Beryllium:
$I$. Beryllium oxide is amphoteric in nature.
$II$. Beryllium hydride is formed by the reaction of beryllium with hydrogen.
$III$. Beryllium hydride is formed by the reaction of beryllium chloride with lithium aluminium hydride.
$IV$. Beryllium sulphate is the least soluble sulphate among the sulphates of alkaline earth metals.

Which of the following elements is chemically most reactive?

What are methanides?

Which element from the following exhibits a diagonal relationship with beryllium $(Be)$?

$A$ compound $(A)$ is used in the preparation of washing soda to recover ammonia in the Solvay process. When $CO_2$ is bubbled through an aqueous solution of $(A)$,the solution turns milky. It is used in whitewashing due to its disinfectant nature. What is the chemical formula of $(A)$?