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 $LiH < NaH < KH < RbH < CsH$.

Which of the following compounds gives oxygen on fast heating?
$I$. $AgNO_3$
$II$. $CaCO_3$
$III$. $Pb(NO_3)_2$
$IV$. $Na_2CO_3$

What is the chemical formula for green vitriol?

Which of the following substances is used as a fertilizer?

Select the correct statement :-
$(a)$ $CaSO_4 \cdot 2H_2O \xrightarrow{393 \ K} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
$(b)$ $3Br_2 + 6NaOH \xrightarrow{\text{hot & conc.}} 5NaBr + NaBrO_3 + 3H_2O$
$(c)$ $3Mg + N_2$ $\rightarrow Mg_3N_2$ $\xrightarrow{6H_2O} 3Mg(OH)_2 + 2NH_3 \uparrow$
$(d)$ $2Be + C$ $\rightarrow Be_2C$ $\xrightarrow{4H_2O} 2Be(OH)_2 + CH_4 \uparrow$
Correct answer is :-

Match the constituents of cements with their percentage proportion :

Constituents	Percentage
$1$. $CaO$	$a$. $2-3\%$
$2$. $MgO$	$b$. $50-60\%$
$3$. $SiO_2$	$c$. $5-10\%$
$4$. $Al_2O_3$	$d$. $20-25\%$