The laughing gas is

The important method for the fixation of nitrogen is

How does concentrated $HNO_3$ react with aluminium?

Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by:

Match the reactions (in the given stoichiometry of the reactants) in List-$I$ with one of their products given in List-$II$ and choose the correct option.

List-$I$	List-$II$
$A. P_2 O_3 + 3 H_2 O \rightarrow$	$1. P(O)(OCH_3)Cl_2$
$B. P_4 + 3 NaOH + 3 H_2 O \rightarrow$	$2. H_3 PO_3$
$C. PCl_5 + CH_3 COOH \rightarrow$	$3. PH_3$
$D. H_3 PO_2 + 2 H_2 O + 4 AgNO_3 \rightarrow$	$4. CH_3 COCl$
	$5. H_3 PO_4$

Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by: