For a good quality cement,the ratio of lime to the total of the oxides of $Si$,$Al$ and $Fe$ should be as close as to :

To distinguish between $A$ and $B$,it is observed that both elements form oxides,but $B$ also forms a nitride when burnt in air. What are $A$ and $B$?

Identify the reactions in which,upon heating,a diatomic gas is evolved,leaving behind a metallic residue.
$(A)$ $2NaN_{3(s)} \xrightarrow{\Delta} 2Na_{(s)} + 3N_{2(g)}$
$(B)$ $Ni(CO)_{4(g)} \xrightarrow{250^{\circ}C} Ni_{(s)} + 4CO_{(g)}$
$(C)$ $2KClO_{3(s)} \xrightarrow{\Delta} 2KCl_{(s)} + 3O_{2(g)}$
$(D)$ $2HgO_{(s)} \xrightarrow{\Delta} 2Hg_{(l)} + O_{2(g)}$
$(E)$ $NH_{4}NO_{2(s)} \xrightarrow{\Delta} N_{2(g)} + 2H_{2}O_{(g)}$

The metal that gives hydrogen gas upon treatment with both acid as well as base is

Copper is very slowly oxidized on the surface in moist air,giving a green coating of verdigris. The chemical formula of verdigris is:

Match the elements given in Column-$I$ with the properties mentioned in Column-$II$ :

Column-$I$	Column-$II$
$A$. $Li$	$1$. Insoluble sulphate
$B$. $Na$	$2$. Strongest monoacidic base
$C$. $Ca$	$3$. Most negative $E^{\circ}$ cell value among alkali metals
$D$. $Ba$	$4$. Insoluble oxalate
	$5$. $6s^2$ outer electronic configuration