Which of the given orders is not correct?

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

'Bordeaux mixture' is used as a fungicide. It is a mixture of

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:

The correct statements among the following are:
$(A)$ $BeH_2$ and $MgH_2$ are polymeric in nature.
$(B)$ $LiH$ is unreactive to oxygen at moderate temperatures.
$(C)$ $BeH_2$ and $MgH_2$ possess significant covalent character.
$(D)$ The stability of alkali metal hydrides follows the order $LiH < NaH < KH < RbH < CsH$.