What is the oxidation number of carbon in methanal?

Which from following is the most commonly used refrigerant Freon-12?

Which among the following salts turns red litmus blue in its aqueous solution?

Identify ' $B$ ' in the following sequence of reactions.

Acetic acid $\xrightarrow[\Delta]{\text { Thionyl chloride }} \mathrm{A} \xrightarrow{\text { Ammonia }} \mathrm{B}$