Which of the following is radioactive?

Atomic hydrogen combines with almost all elements but molecular hydrogen does not. Explain.

The charring of sugar takes place when treated with concentrated $H_2SO_4$. What is the type of reaction involved in it?

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:

The calorific value of producer gas is low because of:

Hydrogen gains an electron to achieve the configuration of a noble gas. It behaves like which of the following?