a student says that all pure substances are elements. do you agree? why or why not? question 14 options: i disagree.  elements form all pure substances, but some pure substances include elements bonded together to form molecules and compounds. i disagree.  all pure substances are also mixtures. i disagree.  elements are not pure substances.  all pure substances include only molecules and compounds, which are more complex. i agree.  pure substances include only single atoms made of one element.

I disagree.  Elements form all pure substances, but some pure substances include elements bonded together to form molecules and compounds.

Explanation:

Pure substances are those that have a uniform and constant (invariable) composition.

That condition is met by both elements and compounds.

Elements are pure substances of one only kind of atoms. For example, gold, oxygen, sodium, hydrogen, are pure substances that arer elements. There are 118 elements known and they are all listed in the periodic table.

Compounds are pure substances formed by two or more different kind of atoms. Water (H₂O), table salt (NaCl), and ethanol (CH₃-CH₂OH), are examples of pure substances that are compounds. There are pratically infinite different compounds.

In conclusion, compounds are also pure substances, since every sample of a given compound has always the same kind of elements bonded in the same way.

wher is the rest of the question

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.