What is the lowest oxidation state possessed by phosphorus in its oxyacids?

Which of the following dissolves in hot conc. $NaOH$ solution?

Give the correct characteristic colours of the products $(P, Q, R, S)$ formed in the following reactions:
$(A)\ NO + NO_2 \xrightarrow{< 250 K} P$
$(B)\ 2 NO_2 \longleftrightarrow Q$
$(C)\ Pb(NO_3)_2 \xrightarrow{673 K} R + PbO$
$(D)\ 4 HNO_3 + P_4O_{10} \longrightarrow S + 4 HPO_3$

Strong reducing behaviour of $H_3PO_2$ is due to

Which of the following is the correct decreasing order of bond angles in the hydrides of group $15$ elements?

Which of the following pairs of oxoacids have a basicity of $2$?