State the valency of each carbon atom in $(i)$ an alkane and $(ii)$ an alkyne.

$(i)$ What is vinegar? State its one use.
$(ii)$ Which gas is produced when dilute ethanoic acid is added to sodium bicarbonate? How will you test the presence of this gas?

$CH_3-CH_2-OH \xrightarrow{\text{Alkaline } KMnO_4 + \text{Heat}} CH_3-COOH$
In the above given reaction,alkaline $KMnO_4$ acts as:

An organic compound $A$ on heating with concentrated $H_2SO_4$ forms a compound $B$, which on addition of one mole of hydrogen in the presence of $Ni$ forms a compound $C$. One mole of compound $C$ on combustion forms two moles of $CO_2$ and $3$ moles of $H_2O$. Identify the compounds $A$, $B$, and $C$ and write the chemical equations of the reactions involved.

What percentage concentration of an aqueous solution of formaldehyde is known as formalin?

Write the number of covalent bonds in the molecule of ethane.