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

• A

  $P$: Blue

  $Q$: Colourless

  $R$: Brown

  $S$: Colourless

• B

  $P$: Colourless

  $Q$: Blue

  $R$: Colourless

  $S$: Brown

• C

  $P$: Colourless

  $Q$: Colourless

  $R$: Blue

  $S$: Brown

• D

  $P$: Brown

  $Q$: Blue

  $R$: Colourless

  $S$: Colourless