Which of the following is dolomite?

Reaction of $BeO$ with ammonia and hydrogen fluoride gives '$A$' which on thermal decomposition gives $BeF_2$ and $NH_4F$. What is '$A$'?

The solubility in water of sulphates down the $Group \ 2$ ($Be$ group) is $Be > Mg > Ca > Sr > Ba$. This is due to

Choose the correct statement$(s)$:
$A.$ Beryllium oxide is purely acidic in nature.
$B.$ Beryllium carbonate is kept in the atmosphere of $CO_2$.
$C.$ Beryllium sulphate is readily soluble in water.
$D.$ Beryllium shows anomalous behavior.
Choose the correct answer from the options given below:

The correct order of density of $Be, Mg, Ca, Sr$ is

Solubility of the alkaline earth metal sulphates in water decreases in the sequence