What is necessary for a metallic bond to form? the atoms should be in close proximity. the atoms should be far apart. the electrons must be attracted to each other. the nuclei must contain neutrons.

The electrons must be attracted to each other.

Answer is: The atoms should be in close proximity.

1. Metallic bond is a type of chemical bond.  

2. Metallic bond is formed between electrons and positively charged metal ions.  

3. Metallic radius is defined as one-half of the distance between the two adjacent metal ions.  

4. Metallic bond increace electrical and thermal conductivity.  

5. Metals conduct heat, because when free moving electrons gain energy (heat) they vibrate more quickly and can move around.

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.