Dihydrogen can be prepared by which of the following reactions?
$(I)$ Reaction of granulated $Zn$ with dil. $HCl$
$(II)$ Reaction of $Zn$ with aq. $NaOH$
$(III)$ By heating calcium hydrogen carbonate

What do you understand by $(i)$ electron-deficient,$(ii)$ electron-precise,and $(iii)$ electron-rich compounds of hydrogen? Provide justification with suitable examples.

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:

Which of the following processes can be used to obtain heavy water $(D_2O)$?

Spin isomerism is shown by

Which chemical is used as a refrigerant in refrigerators?