The number of water molecules in gypsum and plaster of paris respectively are

Which of the following has the lowest solubility?

$A$ white solid '$A$' on heating gives off a gas which turns lime water milky. The residue is yellow when hot but turns white on cooling. This solid '$A$' is

What products are obtained when beryllium oxide is treated separately with aqueous $HCl$ and aqueous $NaOH$ solutions respectively?

$A$ compound $X$ on heating gives a colourless gas. The residue is dissolved in water to obtain $Y$. Excess $CO_2$ is bubbled through the aqueous solution of $Y$ and $Z$ is formed. $Z$ on gentle heating gives back $X$. The compound $X$ is:

The incorrect order of solubility in water is