Which of the following is not a cyclic oxyacid?

What is the similarity between $NH_3$ and $PH_3$?

The passivity of iron in concentrated nitric acid is due to

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

The compound$(s)$ which generate$(s)$ $N_2$ gas upon thermal decomposition below $300^{\circ} C$ is (are)
$A. NH_4NO_3$
$B. (NH_4)_2Cr_2O_7$
$C. Ba(N_3)_2$
$D. Mg_3N_2$

There is very little difference in acid strength in the series $H_3PO_4$,$H_3PO_3$,and $H_3PO_2$ because