NaCl reacts with conc. H 2 SO 4 and K 2 Cr 2 O 7 to give reddish fumes (B), which react with NaOH to give yellow solution (C). (B) and (C) respectively are ;

Step-by-step solution

Chromyl chloride (B) is produced when a chloride ion reacts with conc. H 2 SO 4 and K 2 Cr 2 O 7 . Passing the chromyl chloride gas through NaOH turns the solution yellow. This is due to the formation of Na 2 CrO 4 (C). The reaction is as follows, NaCl + conc . H 2 SO 4 + K 2 Cr 2 O 7 → CrO 2 Cl 2 ( B ) ( Reddish brown ) + KHSO 4 + NaHSO 4 + H 2 O CrO 2 Cl 2 + NaOH → Na 2 CrO 4 ( C ) Yellow Colour + NaCl + H 2 O