1. What is the atomic mass of hydrogen if 99.985% is hydrogen-1 and 0.015% is hydrogen-2?

The atomic mass of Hydrogen : 1.02985

Isotopes are elements that have the same Atomic Number (Proton)  

Atomic mass is the average atomic mass of all its isotopes  

In determining the mass of an atom, as a standard is the mass of 1 carbon-12 atom whose mass is 12 amu  

An atomic mass unit = amu is a relative atomic mass of 1/12 the mass of an atom of carbon-12.  

Mass atom X = mass isotope 1 . % + mass isotope 2.% ..

99.985% is hydrogen-1 and 0.015% is hydrogen-2

The atomic mass of Hydrogen :

b i think it’s a water wheel turning in a stream

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.