What is the molar mass of the third member of a homologous series if the molar mass of the first member is $46 \ g \ mol^{-1}$?

The degree of unsaturation (also known as double bond equivalent or index of hydrogen deficiency) for a compound with the molecular formula $C_{20}H_{22}O_2$ is:

How many secondary carbon and hydrogen atoms are present in the molecule $CH_3-CH(Br)-CH(Br)-CH_3$ respectively?

Which one of the following formulae does not represent an organic compound?

Fill in the blanks:
$(1)$ Two isomers of butane are $n$-butane and isobutane. The relation of the number of $\sigma$ and $\pi$-bonds in them is .......... .
$(2)$ .......... is present in the structure of a heterocyclic compound.
$(3)$ Cyclohexene is a .......... type and furan is a .......... type of compound.
$(4)$ .......... type of $3-D$ model indicates the atomic volume but does not indicate the bond.

How many degrees of unsaturation are there in the following compound?