The class of organic compounds which gives effervescence with $NaHCO_3$ solution is:

What is the molecular formula of vinegar used as a preservative?

An organic compound $A$ of molecular formula $C_{2}H_{4}$ on reduction gives another compound $B$ of molecular formula $C_{2}H_{6}$. $B$ on reaction with chlorine in the presence of sunlight gives $C$ of molecular formula $C_{2}H_{5}Cl$.
$(a)$ Name the compounds $A, B$ and $C$.
$(b)$ Write the chemical equation for the conversion of $A$ to $B$ and name the type of reaction.

What is the role of the metal or reagents written on the arrows in the given chemical reactions?
$(a)$
$(b)$ $CH_{3}COOH + CH_{3}CH_{2}OH \xrightarrow{Conc. H_{2}SO_{4}} CH_{3}COOC_{2}H_{5} + H_{2}O$
$(c)$ $CH_{3}CH_{2}OH \xrightarrow[Heat]{Alkaline KMnO_{4}} CH_{3}COOH$

In electron dot structure,the valence shell electrons are represented by crosses or dots.
$(a)$ The atomic number of chlorine is $17$. Write its electronic configuration.
$(b)$ Draw the electron dot structure of chlorine molecule $(Cl_2)$.

Carbon does not form ionic compounds. Why?