Why does platinum metal make a good catalytic surface for reactant molecules? it causes reactant molecules to be less reactive. it strengthens bonds between reactant molecules. it prevents products from breaking away from the surface. it holds reactant molecules in a good position for them to react.

The right answer is "It holds reactant molecules in a good position for them to react."

Explanation:

Catalysts are a substances that increase the reaction rate by lowering the activation energy (Eₐ) by providing an alternative (lower-energy) pathway for the reaction to take place .

The catalyst increases the frequency of collisions between reactants this done by holding reactant molecules in a good position for them to react.

So, The right answer is "It holds reactant molecules in a good position for them to react."

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.