Write the line notation for a cell in which the cell reaction is as follow
H2 + I2 = 2 HI

I2(g)/I^-(aq)//H2 (g)/H^+(aq)

Explanation:

Let us remember that in every redox reaction, a specie is oxidized and a specie is reduced.

This means that one specie looses electrons while the other species gains electrons.

Considering the overall reaction; H2 + I2 = 2 HI

Oxidation half equation;

H2 (g) > 2H^+(aq) + 2e

Reduction half equation;

I2(g) + 2e > 2I^-(aq)

Line notation;

I2(g)/I^-(aq)//H2 (g)/H^+(aq)

a electronegativity decreases beacuse the size of nucleus is bigger.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.