125C.

Adding a carbon, increases the boiling point incrementally.  In this case, you simply need to

find the midpoint between the boiling points of heptane and nonane.

The intermolecular forces increase as molar mass increases; boiling point increases as a result of these forces.

(2) is the correct answer.

An alkene is a compound in organic chemistry that contains at least one double carbon bond.  If you look at table Q, the general formula of an alkene is

CnH2n.  Choice 2 is the only option which follows this formula.

(2) CH3CH3

A saturated hydrocarbon contains single carbon-carbon bonds (alkane).  You can use the formula from Table Q, CnH2n+2, and see that answer 2 matches this formula.

It is an alcohol.  (check the ending)

1,2-ethanediol is soluble in water because both molecules are polar.