Which of the following orders are correct against the stated property?
$I$) $NaO_2 < KO_2 < RbO_2 < CsO_2$ - stability
$II$) $Mg(OH)_2 < Ca(OH)_2 < Sr(OH)_2$ - basic strength
$III$) $MgCO_3 < CaCO_3 < SrCO_3$ - thermal stability

The two major constituents of Portland cement are

Which pair of substances gives the same gaseous product when they react with water?

Choose the correct statement and mark the correct option given below:
$(a)$ $AgF$ is soluble and colourless in aqueous medium.
$(b)$ For $LiF$,solubility and melting point are both lower as compared to $NaF$.
$(c)$ Solubility of $Rb_2SO_4$ is less as compared to $BaSO_4$.
$(d)$ If $AgI$ is added to water,the colour of water will turn yellow from colourless.

Give a brief account of the abundance of alkali metals and alkaline earth metals in the Earth's crust.

$A$ white solid '$A$' on heating produces a gas that turns lime water milky,and the remaining solid residue is yellow when hot but turns white on cooling. The solid '$A$' is: