The end product $(B)$ of the above reaction is:

• A
  $2$,$2$'-diformylbiphenyl
• B
  $2-$carboxy-$2$'-hydroxymethylbiphenyl potassium salt
• C
  $2$,$2$'-bis(hydroxymethyl)biphenyl
• D
  $2$,$2$'-dicarboxylbiphenyl dipotassium salt