What is the name of the aldehyde corresponding to methane?

An atom of an element contains six electrons in its valence shell. This element is the second major component of air. It exists as a diatomic molecule.
$(i)$ Identify the element.
$(ii)$ Show the bond formed between two atoms of this element.
$(iii)$ Write the nature of the bond between the two atoms.

Which compound contains the $-COOH$ functional group?

The first member of the alkyne homologous series is:

$C_{3}H_{6}$,$C_{4}H_{8}$,and $C_{5}H_{10}$ belong to the same homologous series.
$(i)$ Define homologous series.
$(ii)$ Why are the melting and boiling points of $C_{5}H_{10}$ higher than $C_{4}H_{8}$?
$(iii)$ Arrange these hydrocarbons in order of increasing boiling points.

What is the common name of ethanal?