Write a short note on Dihydrogen.

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Isotopes of hydrogen have almost same chemical properties,but difference in their rates of reaction.
Reason $R:$ Isotopes of hydrogen have different enthalpy of bond dissociation.
In the light of the above statements,choose the most appropriate answer from the options given below:

With which of the following does hydrogen combine directly?

The gaseous product$(s)$ expected at room temperature by the reaction of sodium borohydride and boron trifluoride under anhydrous conditions is/are:

Asthma patients use a mixture of $.....$ for respiration.

Which of the hydrogen halides forms salts like $KHX_2$ (where $X$ is a halogen atom)?