13. which statement about an element's average
atomic mass is correct?
a) the more isotopes of a given element, the
higher the average atomic mass
b) it is calculated by taking the average atomic
number of a given element
c) it is a weighted average, so abundant
isotopes have a greater effect than
uncommon ones
d) the atomic number is always larger than the
average atomic mass

answer:

i believe its a

plz mark brainliest i need 1 more

explanation:

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.