Click on the diagram to choose which atom is more reactive. Hint: These are nonmetals. Which is going to gain a full valence shell of 8 electrons the easiest?

The first one has 5 valence electrons, and the second has 7. (This can be counted by counting the amount of black dots on the biggest circle). Since 7 > 5, it would be easier for the second one to gain one (so that it completes it's valence shell) so the answer is the second one.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.

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.