What is the chemical formula for green vitriol?

Arrange the following in the correct order of thermal stability:
$K_2CO_3, MgCO_3, CaCO_3, BeCO_3$

Which orders are correct?
$(I)$ Thermal stability: $BeSO_4 < MgSO_4 < CaSO_4 < SrSO_4$
$(II)$ Basic nature: $CaO > MgO > BeO > ZnO$
$(III)$ Solubility in water: $LiOH < NaOH < KOH < RbOH$
$(IV)$ Melting point: $NaCl > KCl > RbCl > CsCl > LiCl$

Which of the following does not dissolve in dil $H_2SO_4$?

Holme's signals can be obtained by using

Consider three metal chlorides $x$, $y$ and $z$, where $x$ is water soluble at room temperature, $y$ is sparingly soluble in water at room temperature and $z$ is soluble in hot water. $x$, $y$ and $z$ are respectively: