How many moles of hydrogen gas(H2) are needed to react with 15 moles of chlorine gas

15 moles of hydrogen gas are needed to react with 15 moles of chlorine gas.

Explanation:

The balanced reaction is:

H₂ (g) + Cl₂ (g) → 2 HCl (g)

By stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of the compounds participate in the reaction:

Then you can apply the following rule of three:  If 1 mole of Cl₂ reacts with 1 mole of H₂, 15 moles of Cl₂ with how many moles of H₂ does it react?

moles of H₂= 15

15 moles of hydrogen gas are needed to react with 15 moles of chlorine gas.

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.