Why does earth’s rotation axis lean toward the sun for only one-half of its orbit?

The earth is inclined to the plane of its orbit by 23.5 degrees. Therefore for half the time in its earth on its orbit, the north pole will be inclined towards the sun. During this period, the pole receives six months of continuous sunshine. In the other half of the revolution around the sun, the north pole is tilted away from the sun hence receives darkness for 6 months.

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.