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2.5 moles of O₂ = 5 moles of H₂O

Explanation:

The balanced equation for the reaction is given below:

2H₂ + O₂ —> 2H₂O

From the balanced equation above,

1 mole of O₂ reacted to produce 2 moles of H₂O.

Finally, we shall determine the number of mole of H₂O produced by the reaction of 2.5 moles of O₂. This can be obtained as follow:

From the balanced equation above,

1 mole of O₂ reacted to produce 2 moles of H₂O.

Therefore, 2.5 moles of O₂ will react to produce = 2.5 × 2 = 5 moles of H₂O.

Thus,

2.5 moles of O₂ = 5 moles of H₂O

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.